当……时
Reach for 当……时 when you want to set a precise time-frame for an event — 'when X happened, Y was happening too.' It's the literary version of plain 的时候: same meaning, more polish. You see it constantly in news leads and narrative writing because it lets the writer freeze a moment ('when the plane touched down at Beijing Capital Airport…') before delivering the next line. In speech, people skip the 当 and just say 时候.
Structure
当 [EVENT/TIME] 时, [MAIN CLAUSE]
dāng... shí...
How to Think About It
当 and 时 are bookends, not a single word. 当 opens the time-frame and 时 closes it — everything between them is the moment being framed. Think of it as cinematic framing: 当 says 'open the shot,' 时 says 'and now the camera cuts to what happens.' The main clause always comes after 时, never before, because the time-frame has to be set up first.
Examples
当我走进教室时，老师已经在讲课了。
Dāng wǒ zǒu jìn jiàoshì shí, lǎoshī yǐjīng zài jiǎngkè le.
When I walked into the classroom, the teacher was already lecturing.
当夜幕降临时，城市亮起了灯光。
Dāng yèmù jiànglín shí, chéngshì liàng qǐ le dēngguāng.
When night fell, the city lit up.
当他听到这个消息时，眼泪流了下来。
Dāng tā tīng dào zhège xiāoxi shí, yǎnlèi liú le xiàlái.
When he heard the news, tears rolled down his face.
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 because English 'when' is one word. 当……的时候 also works, but 当 alone without 时 or 的时候 dangles — the time-frame never closes.
当他到家，已经很晚了。
当他到家时，已经很晚了。
Don't Confuse With
……的时候
Colloquial equivalent. 当……时 belongs to news and essays; 的时候 belongs to conversation.
一……就……
Use 一……就…… for 'as soon as A, B' — tight sequencing. 当……时 just sets a backdrop without implying immediacy.
在……时
在……时 emphasizes the duration of an ongoing situation; 当……时 zooms in on a specific moment when something happened.
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.
Practice
____我醒来时，天已经亮了。
Show answer
当
当电话响起____，他正在洗澡。
Show answer
时
Arrange: 时 / 当 / 下雨 / 开始 / 我们 / 出门了
Show answer
当开始下雨时，我们出门了。
Translate: When the news broke, everyone fell silent.
Show answer
当消息传出时，所有人都安静了下来。
Write one sentence using 当……时 to describe a memorable moment.
Show answer
当我第一次踏上长城时，我感到非常震撼。
Fill in: ___ 我到家 ___，妈妈已经睡了。
Hear It in Real Episodes
This pattern appears in 2 Fluentide episodes:
当弗里德里希·默茨的专机穿过云层，缓缓降落在北京首都国际机场时
当我们把视线从全球总榜稍微偏移，看看同样极具参考价值的Billboard Global Excl. U.S.，也就是除美全球单曲榜时，另一位超级巨星的名字赫然在列。
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.