防微杜渐（防微杜漸）　

◎ 防微杜渐 fángwēi-dùjiàn

[arrest what seems to be the begining of an unwholesome trend;check erronrous ideas at the outset] 当坏事、坏思想、坏作风刚刚冒头的时候,就加以制止,不让它发展下去