to allow someone to do what they want in a place

You don't want to let Oliver loose in the kitchen. 你不想让奥利弗在厨房里到处乱跑吧。

If you let loose something such as bullets or bombs, you release a lot of them all together.

The allies let loose an intensive artillery bombardment over the border. 联军对边境地区进行了一阵猛烈的炮击。

to suddenly make a sound or speak in an uncontrolled way

He turned around and let loose a torrent of abuse. 他转过身来破口大骂。