In this study, a systematic observation of a passively Q-switched Nd:YVO4 laser by varying initial transmission of saturable absorbers and reflectance of output couplers. When the reflectivity of the output coupling mirror is 70% and the initial transmission of Cr:YAG is 67%, the laser performance such as the pulse energy, pulse width, and peak power are 4.38μJ, 6.65ns, and 659.1W, respectively. The rate equations of passive Q-switched laser are used to simulation the influence between the reflectance of output mirror and laser properties.