The experimental study of the double-pass grazing incidence Nd:YVO₄ slab amplifier is carried out based on a saturable absorber and passively Q-switched microchip seed laser. The microchip laser with pulse duration of 90 ps, repetition rate of 100 kHz and beam quality factor M²=1.16 acts as seed laser with varying output power from 100 μW to 10 mW. The new liquid pure metal grease and the traditional thin indium foil are used to conduct as the thermal contact material of the bounce amplifier, respectively. Experimental results show that the liquid pure metal grease conducted as the thermal contact material can significantly reduce the temperature of the slab pump face. An output power of 13 W is obtained with the liquid pure metal grease conducted as the thermal contact material for 10 mW seed power with pump power of 55 W at an optical-optical efficiency of 23%, achieving pulse peak power of 1.2 MW and pulse energy of 130 μJ. The beam quality factor is M²_x=1.30,M²_y=1.28.