Rack server capable of detaching a replaceable module conveniently

A rack server includes a replaceable module, and a frame for supporting the replaceable module. Two slots are formed on both sides of the frame respectively. The rack server further includes a cover installed on the slots in a slidable manner. The cover includes a first housing and a second housing pivoted to the first housing. When the second housing rotates to a first position relative to the first housing, the second housing covers the replaceable module. When the second housing rotates to a second position relative to the first housing, the second housing cannot cover the replaceable module. The rack server further includes a first fixing mechanism installed on a side of the slot of the frame for fixing the second housing on the frame when the second housing rotates to the first position relative to the first housing.