The pulses with energy of 3.5 mJ,repeatition rate of 1～100 Hz and energy fluctuation less than 1% have been obtained of a slab Nd:YAG laser pumped by a quasi-CW 60 W laser diode array. The optical to optical efficiency is 15% and slop efficiency is 29%. The Q-switchings of the DPL involving A-O, E-O, and color center crystals and dye have been realized respectively. The maximum peak output power of the laser is 100 kW.