By considering the Gaussian spatial distribution of the intracavity photon density and the thermal effect in the gain medium,the coupled rate equations of a LD-pumped passively Q-switched Nd∶GdVO_4 laser at 1.06 μm with Cr 4+ ∶YAG are given. The theoretical pulse width,pulse repetition rate,single-pulse energy, and peak power of the laser are obtained by numerically solving the rate equations.The theoretical calculations agree with the experimental results.