Abstract: A mathematic model of passive self-Q-switched microchip laser under pre-pumping mechanisms was presented. Using this model, the repetition rate, pulse width and peak power of laser pulses train were accurately obtained under given pumping conditions. In order to examine the model, the experiments of pre-pumping passive Q-switched Cr4+,Nd3+:YAG lasers were designed under corresponding pumping conditions. The experimental results agree well with the numerical simulation results. It illuminates that peak power of the laser pulses increases along with the rising of entire pumping rate; however, laser pulse width decreases as the entire pumping rate rises. Both speeds of decrease and increase slow down when the entire pumping rate goes far from the threshold. Moreover, the deviation between the