Parasitic oscillation in the slab amplifier affects the efficiency of laser amplifier and reduces the stored energy of slab crystal. The surface of Nd:YVO4, gain of grazing incident slab amplifier was processed to suppress the parasitic oscillation in the slab and improve the energy storage ability of slab crystal. Through ion sputtering method, the germanium was plated on top and bottom surface and the back surface to suppress the parasitic oscillation. In germanium plated and without germanium plated conditions, the slab oscillator′s output characteristics were compared between free oscillation and Q-switched mode, threshold current reduced 15% in plating germanium slab oscillator, and the stored energy improved 86.9%. The beam quality, pulse duration and spot pattern of plating germanium slab oscillator were basically the same to without plating germanium slab oscillator in Q-switched mode. Experimental result indicates plating germanium on the face of slab is an effective method to suppress the parasitic oscillation and improve the energy storage ability of crystal.