If a period of time or series of events leads up to an event or activity, it happens until that event or activity begins.

The pilot had no recollection of the events leading up to the crash. 飞行员想不起飞机坠毁前发生了什么。

to prepare to talk about something by gradually mentioning the subject you want to talk about

He started telling me about a wonderful new restaurant he'd been to and I wondered what he was leading up to. 他开始跟我讲他去过的一家很棒的新餐馆，而我则在想他到底想要说什么。