A computer case includes a first sidewall, a plurality of peripheral walls, a retractable fence, and a second sidewall. One side of each of the peripheral walls connects with the first sidewall in a surrounding manner; one end of the retractable fence is disposed to the other side of each of the peripheral walls. The retractable fence is able to reciprocate along an extending direction of the peripheral walls. Besides, the second sidewall connects with the other end of the retractable fence in a surrounding manner. An inner space of the computer case is selectively increased or decreased by the reciprocating of the retractable fence for replacing a cooling module or an electronic component with different width.