If unwanted people or things overrun, they fill a place quickly and in large numbers.

Rebel soldiers overran the embassy last night. 昨晚叛乱士兵占领了大使馆。

Our kitchen is overrun with cockroaches. 我们的厨房蟑螂横行。

to continue past an intended limit, especially a finishing time or a cost

My evening class overran by ten minutes. 我的夜校课晚下课了10分钟。

It looks as if we're going to overrun our budget. 看上去我们要超出预算了。