In this paper the performance of a Cr 4+ :YAG passively Q-switched diode laser pumped QCW slab Nd:YAG laser with a repetition rate of 100 Hz is reported. The dependence of the pumping threshold, the pulse width, the average output power as well as the energy extraction efficiency of Q-switched pulses on input pump pulsewidth was observed. A pulse width (FWHM) of 37.4 ns of the Q switched laser was obtained. The laser system operated very stably.