The experiment on high pumped Nd:YAG laser passively Q!switched by Cr:YAG is carried out.Especially, the influence of pump power,cavity length,the output coupler transmittance, and the distance between Nd:YAG and Cr:YAG on the repetition rate, pulse width, and peak power instability of laser output is investigated. The experimental results are analyzed and discussed. It is shown by the curve that pumping power is the main factor, the increasing pumping power and decreasing cavity length result to an increasingly instable output, there is an optimized output coupler transmittance which makes the output laser pulse stablest. Phenomena observed in the experiment is analyzed based on the theory of passively Q!switched, and the results could be used in the designing of same lasers.