当... 时，...
Reach for this when you want to anchor an event to a specific time frame — 'when X happens / happened, Y...' The 当...时 bracket sets the scene; the main clause follows after the comma. Slightly more formal than plain 的时候 — common in narration, history writing, news, and reflective prose ('when I was a child...,' 'when the policy came into effect...'). In speech, 的时候 covers most of the same ground; reach for 当...时 when you want a touch more weight or rhythm.
Structure
当 + Clause + 时(候)，Main Clause
dāng... shí (hou)
How to Think About It
Think of 当...时 as a pair of brackets around the time frame. 当 opens the time clause; 时 (or 时候) closes it. Whatever sits between them is the 'when.' The main statement comes after. English does the same thing with 'when... ,' but Chinese requires both bookends for the formal version — drop one and the sentence feels unbalanced. 的时候 is the casual one-token equivalent: 我小的时候 vs 当我小的时候 (slightly more literary).
Examples
当我还是个孩子时，我们家住在乡下。
Dāng wǒ háishì gè háizi shí, wǒmen jiā zhù zài xiāngxià.
When I was still a child, our family lived in the countryside.
当老师走进教室时，学生们都站了起来。
Dāng lǎoshī zǒu jìn jiàoshì shí, xuéshēngmen dōu zhàn le qǐlái.
When the teacher walked into the classroom, the students all stood up.
当政策正式实施时，市场反应非常迅速。
Dāng zhèngcè zhèngshì shíshī shí, shìchǎng fǎnyìng fēicháng xùnsù.
When the policy formally took effect, the market reacted very quickly.
当你遇到困难时，记得给我打电话。
Dāng nǐ yùdào kùnnán shí, jìde gěi wǒ dǎ diànhuà.
When you run into trouble, remember to call me.
Common Mistake
Learners forget the closing 时/时候 because English 'when' is a single word. Chinese 当...时 is a paired bracket — both ends are required.
当我回家，我妈妈在做饭。
当我回家时，我妈妈在做饭。
Don't Confuse With
的时候
Casual everyday 'when.' Same meaning, less formal. 我小的时候 vs 当我小的时候 — the second sounds slightly more written/reflective.
一...就...
'As soon as X, then Y' — emphasizes immediate sequence. 当...时 sets a background frame; 一...就... triggers a quick follow-up.
在...的时候
Adds 在 for extra emphasis on 'during.' Largely overlaps with 当...时. 在...的时候 leans spoken; 当...时 leans written.
Practice
Fill in: ___ 我到家 ___，妈妈已经睡了。
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当 / 时
Arrange: 当 / 我 / 时 / 五岁 / ， / 我 / 在 / 北京 / 住
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当我五岁时，我住在北京。
Translate to Chinese: When the alarm rang, I was still asleep.
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当闹钟响时，我还在睡觉。
Use 当...时 to describe what you were doing at a specific moment in the past.
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当地震发生时，我正在办公室开会。
Hear It in Real Episodes
Related Grammar Patterns
Acquire by listening
Hear 当... 时，... in real Chinese, not in a textbook.
Fluentide picks the next news episode at your level, so this pattern shows up again and again in real context. The transcript marks it, the audio drills it. Free to start, no card.