The diode laser side pumped 1 kHz E-O Q-switched TEM00 mode laser was studied. The single pulse energy of laser is 0.712 mJ and 10 ns pulse width. Three types of cooling Nd:YAG slab were used in the experiment for comparison. Experimental results show that the thermal effect in diode pumped Nd:YAG slab affects laser efficiency in its high repetition rate operation. The results obtained are applicable to the design of high-power diode laser pumped laser system.