一…就…: as soon as…
固定格式 / fixed patterns
Tone colorsā tone 1á tone 2ǎ tone 3à tone 4a neutral
Subject + 一 + V1，(Subject) + 就 + V2
一 A 就 B: "as soon as A, B". The two actions follow immediately, or B happens every time A does.
一 and 就 are adverbs: they go before the verbs, after any subject: 我一到就给你打电话.
Great for directions: 你一出门就能看见 (you'll see it as soon as you step out).
Examples
我一到就给你打电话。
Wǒ yí dào jiù gěi nǐ dǎ diànhuà.I'll call you as soon as I arrive.
你一出地铁站就能看见那个商场。
Nǐ yì chū dìtiězhàn jiù néng kànjiàn nàge shāngchǎng.As soon as you exit the subway, you'll see the mall.
他一下班就回家了。
Tā yí xiàbān jiù huí jiā le.He went home as soon as he finished work.
我一喝咖啡就睡不着。
Wǒ yì hē kāfēi jiù shuì bu zháo.Whenever I drink coffee, I can't sleep.
Common mistakes
✗ 一我到就… → ✓ 我一到就… (一 after the subject).
With two subjects: ✗ 我一到，就他来了 → ✓ 我一到，他就来了.
Mind the tone change of 一: yí before a 4th tone, yì before the others.