A power transmission structure of a power supply unit includes a base plate. The base plate is provided with a plurality of spaced metallic plates. One end of each metallic plate is provided with a first connecting portion and the other end is provided with a second connecting portion to connect the components of the power supply unit respectively for power transmission. Thus, the present invention can take the place of conventional power cords, and the power transmission structure can be flattened to decrease the space occupied by the power transmission device, such that the required interior accommodation space of the power supply unit can be decreased effectively and the volume of the power supply unit can be reduced.