An assembly device for a computer case and outer cover incorporating: a host case provided with a bottom plate and perpendicular left and right side walls, a circuit motherboard fixed within the holding space, a jack panel of relatively small area and size is located at a tail end of the circuit motherboard, and an electrical circuit is printed on an inverse side of the jack panel; a rectangular outer cover, the outer cover can be assembled/disassembled to/from the rectangular gap of the host case, and the jack panel can be plugged into or withdrawn from the socket, thereby realizing a rapid and convenient method of assembling and disassembling the outer cover to and from the host case.