The pulse output characteristics of Cr4+∶YAG passive Q-switched laser were studied.The effects of initial transmittance and crystal length of Cr4+∶YAG on the laser output pulse width were simulated by the rate equation model of Cr4+∶YAG transition absorption.The Nd∶YAG laser pumped by xenon lamp is used for passive Q-modulation experiment.Combined with the simulation results,the phenomenon of generating laser multi-pulse is analyzed.By optimizing the passive Q-switching parameters,a stable laser pulse output with a laser pulse width of about 17.5 ns and single pulse energy of 195 mJ is obtained.