Passive Q-switching of LD-pumped Nd: YVO 4 laser was demonstrated with a GaAs wafer as saturable absorbers in a plane-concave cavity. The pulse characteristics of passive Q-switched Nd: YVO 4 laser with a GaAs were measured. Q-switched pulse duration is 15 ns, pulse repetition rate is 470 kHz, beam quality M2 is equal to 1.31 and laser threshold of passive Q-switching is 500 mW. The numerical calculations of rate equations for case of GaAs playing the role as mentioned above are performed, and passive Q-switched mechanism and the dependency of pulse duration and pulse repetition rate on pumping rate are discussed. The calculated result was well in agreement with the experiments results.