As soon as… then… (一…便)

Structure 一 + action 1 + 便 + action 2

一…便… (yī… biàn…) links two near-simultaneous events: «as soon as A (happens), B (right after)». It is the formal, written variant of 一…就… (HSK 3, id hsk3-yi-jiu): same meaning and structure, but with 便 instead of 就. 便 belongs to journalism, essays and literary narration; 就 is the neutral, everyday register. The link is still one of immediacy: the second action occurs the moment the first is complete.

Examples

他tā一yī进jìn门mén便biàn察chá觉jué了le异yì样yàng。
The moment he stepped through the door, he sensed something was off.
消xiāo息xī一yī传chuán出chū，便biàn引yǐn起qǐ了le轩xuān然rán大dà波bō。
As soon as the news got out, it caused a great uproar.
会huì议yì一yī结jié束shù，他tā便biàn匆cōng匆cōng离lí去qù。
As soon as the meeting ended, he hurried off.
天tiān一yī亮liàng，村cūn民mín便biàn纷fēn纷fēn下xià地dì劳láo作zuò。
As soon as day broke, the villagers went down one after another to work the fields.

Levels are indicative: they follow the standard Chinese Grammar Wiki (AllSet Learning) progression, not an official HSK 3.0 mapping. We never assign levels by eye.

This point and the other 370, with audio on every example, inside Wanyu.