当 Introducing a Time Setting in Chinese
当 + 时间
The preposition 当 introduces the time setting in which another event occurs. It commonly precedes a clause and combines with 的时候 or 时 before the main clause. The entire time phrase comes before the event it frames. This is different from 当 meaning to serve as or become something.
Published July 31, 2026
Reviewed July 31, 2026
01 / PATTERN
See the Structure
MODEL
当 + Clause + 的时候 / 时，Main Clause
Read the structure
The preposition 当 introduces the time setting in which another event occurs. It commonly precedes a clause and combines with 的时候 or 时 before the main clause. The entire time phrase comes before the event it frames. This is different from 当 meaning to serve as or become something. Keep the model 当 + Clause + 的时候 / 时，Main Clause visible while you compare each sentence.
当他进来的时候，我们正在看电视。
When he came in, we were watching television.
Choose the right context
Introduce the time at which a main event occurs. Build 当……的时候 before a following clause. Use concise 当……时 in more compact writing.
当我到家的时候，天已经黑了。
When I got home, it was already dark.
Respect the boundary
Do not place 当 after the completed time phrase. Do not leave 当 without a following time expression or clause. Do not confuse time-introducing 当 with the verb meaning serve as.
他进来的时候当，我们正在看电视。
(He came in when dang, we were watching television.)
Repair the pattern
当 is stranded after the time clause: 当 must introduce the time clause instead of following the completed 的时候 phrase. 当 lacks the clause that supplies its time setting: The preposition 当 must be followed by the event used as the time setting.
当他进来的时候，我们正在看电视。
Use the repaired structure without changing the intended meaning.
02 / MAP
Read the Sentence
Read from left to right and notice the job performed by each part. The labels describe this example; they are not a rule that every Chinese sentence must copy.
当他进来的时候，我们正在看电视。
When he came in, we were watching television.
当
当
This part occupies the 当 position in the model pattern.
他
Clause
This part occupies the Clause position in the model pattern.
进来
的时候 / 时，Main Clause
This part occupies the 的时候 / 时，Main Clause position in the model pattern.
的
当
This part occupies the 当 position in the model pattern.
时候
Clause
This part occupies the Clause position in the model pattern.
，
的时候 / 时，Main Clause
This part occupies the 的时候 / 时，Main Clause position in the model pattern.
我们
当
This part occupies the 当 position in the model pattern.
正在
Clause
This part occupies the Clause position in the model pattern.
看
的时候 / 时，Main Clause
This part occupies the 的时候 / 时，Main Clause position in the model pattern.
电视
当
This part occupies the 当 position in the model pattern.
03 / EXAMPLES
Examples You Can Reuse
Keep the structure stable while changing the people, objects, times, or conditions. Pinyin is shown as reading support; use the Chinese sentence and translation to confirm the grammar relationship.
当他进来的时候，我们正在看电视。
When he came in, we were watching television.
当我到家的时候，天已经黑了。
When I got home, it was already dark.
当比赛结束时，大家都站了起来。
When the match ended, everyone stood up.
04 / LIMITS
When to Use It — and When Not To
Use it when
- Introduce the time at which a main event occurs.
- Build 当……的时候 before a following clause.
- Use concise 当……时 in more compact writing.
Do not use it when
- Do not place 当 after the completed time phrase.
- Do not leave 当 without a following time expression or clause.
- Do not confuse time-introducing 当 with the verb meaning serve as.
05 / REPAIR
Compare Right and Wrong
Compare the smallest meaningful change. Each explanation identifies a placement, scope, form, or clause relationship instead of treating the whole sentence as one undifferentiated mistake.
他进来的时候当，我们正在看电视。
当他进来的时候，我们正在看电视。
当 is stranded after the time clause
当 must introduce the time clause instead of following the completed 的时候 phrase.
当的时候他进来，我们正在看电视。
当他进来的时候，我们正在看电视。
当 lacks the clause that supplies its time setting
The preposition 当 must be followed by the event used as the time setting.
他进来的时候当，我们正在看电视。
当 must introduce the time clause instead of following the completed 的时候 phrase.
当的时候他进来，我们正在看电视。
The preposition 当 must be followed by the event used as the time setting.
06 / PRACTICE
Practice the Grammar Point
Complete three short tasks in order: judge the pattern, repair a common error, and build the sentence. Feedback is fixed and reviewed, so these activities do not use a checker allowance.
1. Judge the sentence
2. Choose the correction
3. Build the sentence
Build a complete sentence with 当 + 时间.
07 / APPLY
Apply It in Your Sentence
Write one original sentence with 当 + 时间. Your draft moves to the checker through this browser session, selects this grammar point as the first review focus, and waits for you to submit.
08 / QUESTIONS
当 Introducing a Time Setting Questions
Can 当 be followed by 时 instead of 的时候?
Yes. 当……时 is a compact alternative, especially in writing, while 当……的时候 is common in speech.
Does 当 always introduce time?
No. 当 also has verbal uses such as serving as something; this lesson covers only the time-setting preposition.
09 / SOURCES
Sources and Review Notes
These references support different parts of the lesson. GF0025-2021 supports level placement only; professional grammar works support the explanation, limits, examples, and cross-checks. Their inclusion does not imply endorsement.
Chinese Proficiency Grading Standards for International Chinese Language Education (GF0025-2021)
Ministry of Education and State Language Commission · Ministry of Education of the PRC · 2021
Locator: Appendix A, Level 2 item 【二21】, PDF p. 188
Lists 当 among Level 2 prepositions that introduce time and gives 当……的时候 examples.
Official source现代汉语语法课程讲义
包头师范学院 · 包头师范学院 · 2024
Locator: Course PDF pp. 17–18, prepositions and prepositional phrases
Defines prepositions as preceding their complements and forming pre-predicate adverbial phrases that can mark time.
Official source10 / CONTINUE
Continue with a Connected Rule
Compare
时间Time Word Placement
Place the whole 当 time clause before the main event using established temporal order.
Learn first
副词、形容词、时间和处所词语作状语Basic Adverbial Order Before the Predicate
Review the broader pre-predicate position shared by time, place, and manner adverbials.
Compare
在在 for Location and the Setting of an Action
Compare a clause-level time setting introduced by 当 with a location setting introduced by 在.
Continue learning
年 / 月 / 日；点 / 分Clock and Calendar Order
Continue from calendar expressions to a full event used as a contextual time setting.
RECOMMENDED NEXT
Compare
Place the whole 当 time clause before the main event using established temporal order.