A computer casing has a frame, two fixing panels arranged inside the frame, and two side panels assembled on opposing sides of the frame. The frame, the fixing panels and the side panels are all made of aluminum. The frame includes a top panel, a bottom panel, a front panel and a rear panel fixed together by means of soldering. The computer casing is secured in entirety and has large dissipation area. Additionally, the computer casing is easily classified and recycled in the case of expiration.