A hinge assembly includes a pivot shaft, a rotatable stand, a fixed stand, a cam, a cam follower, and a fastening member. The rotatable stand is non-rotatably connected to the pivot shaft and has a first fixing plate. The fixed stand is rotatably connected to the pivot shaft, and has a second fixing plate. The fastening member engages with an end of the pivot shaft. The cam follower defines two positioning cutouts. Two positioning protrusions are formed on the cam. One of the cam and the cam follower is rotatably connected to the pivot shaft. When the positioning protrusions engage in the positioning cutouts, the first fixing plate is oblique to the second fixing plate.