Using crystal electro-optic effect Q-switched pulse (PRM)was made,the realization of resonator mirror reflection of the part of a laser oscillation.Laser medium for Nd∶YAG,300W LDA（laser diode array）end-pumped continuous surface and micro-lens and lens catheter optical coupling efficiency of 75% transmission,for the electro-optic crystal KDP,Ping-cavity structure,dielectric cavity placed polarizer,cavity length 11cm,the withdrawal pressure-Q-switched,a practical design of the retreat pressure Q-switched circuit,Q-switch along the trigger,improved low-light silicon photodiode measurement circuit,the output pulse modulation,the output pulse width 11ns,light-light conversion efficiency of 10.8%,the output-4 mJ pulse energy,the experimental results are analyzed and discussed.