The invention discloses a side-feed supply device for a pulsed plasma electric thruster. The side-feed supply device comprises two sets of supply assemblies of symmetric structures, the supply assemblies are fixedly connected to a bottom plate of the electric thruster, the supply assemblies comprise a first supply bracket, a first tension spring, a first push rod, a first supply blocking sheet, afirst solid propellant, a second supply bracket, a second tension spring, a second push rod, a second supply blocking sheet and a second solid propellant, the opposite ends of the first solid propellant and the second solid propellant are of bevel structures which constitute a V-shaped discharge groove, an opening of the V-shaped discharge groove faces the tail end of an electrode plate, and a cone limiting table is arranged at the position, at the included angle of the V-shaped discharge groove, of the inner side of an anode plate. According to the side-feed supply device, the two solid propellants can be fed, a V shape is constituted by the ablation end faces of the propellants in a discharge room, thus the area swept by an electrical discharge arc can be increased, and the ablation quality of single pulse under the same condition is also improved.