X 一 + Verb1, 就 + Verb2
Reach for 一...就... when one thing triggers another with no gap — 'the moment X happens, Y immediately follows.' It's how Chinese says 'as soon as.' Equally good for habits ('every time he sits down he falls asleep'), one-off events ('the moment I got home I called you'), and quick reactions ('one sip and I knew it was bad').
Structure
[SUBJECT] 一 [VERB 1], 就 [VERB 2]
yī [VERB1], jiù [VERB2]
How to Think About It
一 isn't 'one' here — it compresses Verb 1 into a single trigger event. 就 then announces the result happens fast, with no buffer. The pair acts like a domino: tip one, the next falls. If you replace 就 with 才, you flip the speed entirely — 才 means it took a long time, the OPPOSITE feel. Watch the subject: usually one subject does both verbs, but two subjects also work ('他一回来我就走').
Examples
我一到家就给你打电话。
Wǒ yī dào jiā jiù gěi nǐ dǎ diànhuà.
I'll call you the moment I get home.
他一喝咖啡就睡不着。
Tā yī hē kāfēi jiù shuì bù zháo.
He can't sleep whenever he drinks coffee.
孩子一看到妈妈就笑了。
Háizi yī kàn dào māma jiù xiào le.
The moment the child saw mom, he smiled.
Common Mistake
Learners use 一...就... for any 'when' clause, even slow or vague ones. It specifically signals immediacy — if the gap could be hours or there's no real trigger, use 当...的时候. Also: don't add 了 to Verb 1; the 一 already handles the completion feel.
我一下班了, 就去吃饭。
我一下班, 就去吃饭。
Don't Confuse With
当 ... 的时候
Neutral 'when' — no rush implied. Use 当...的时候 when the two events happen in the same window but you're not claiming one triggered the other instantly.
一 ... 才 ...
Sounds parallel but flips the speed: 才 = finally, only then. '我等了一个小时才到' (I waited an hour before he arrived). Don't mix 一...就 (fast) and ...才 (slow).
只要 ... 就 ...
Both use 就, but 只要 is conditional ('as long as'), not temporal. '只要你来, 就能见到他' = condition. '你一来就能见到他' = the moment you arrive.
Practice
我 ___ 听到这个消息就告诉你。
Show answer
一
他一坐下 ___ 开始玩手机。
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就
Put in order: [我 / 一 / 就 / 累 / 想睡觉]
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我一累就想睡觉。
Translate to Chinese: 'As soon as it rains, the road gets crowded.'
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一下雨, 路上就堵车。
Write one sentence about a habit or quick reaction, using 一...就....
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Example answer: 我一紧张就忘词。 (The moment I get nervous, I forget my lines.)
Hear It in Real Episodes
This pattern appears in 2 Fluentide episodes. Press play to hear the sentence:
他自己没感觉，等到出了海，他才开始病。
He himself didn't feel it, and only started getting sick once they were at sea.
MV Hondius Hantavirus Outbreak Strands 147Intermediate
所以鲨鱼一闻到，就都过来了。
So as soon as they smell it, they all come over.
Sperm Whale Carcass Closes Four Sydney BeachesIntermediate
Related Grammar Patterns
Acquire by listening
Hear X 一 + Verb1, 就 + Verb2 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.