A lamp, a lamp system, a method for assembling lamp system, and a method for disassembling lamp system are described. The lamp includes a frame, a light guide plate, at least one light source and a connecting mechanism. The frame includes two side covers opposite to each other, and an accommodating space is formed between the side covers. The light guide plate is disposed in the accommodating space. The light source is disposed in at least one of the side covers and is disposed adjacent to a light incident surface of the light guide plate. The connecting mechanism is disposed in the frame. The connecting mechanism includes an engaging member and an adjusting member. The engaging member is slidably disposed in an inner space of one of the side covers.