In this paper, we compare pulse parameters in two end-pumped passively Q-switched lasers by increasing the boundary temperature of the laser crystal. For the Nd:YAG/Cr:YAG laser, the pulse energy at 1 kHz increased from 12.4 to 21 μJ when the boundary temperature increased from 20°C to 120°C, while the pulse width decreased by 1.2 times. For the Nd:YVO4 passively Q-switched laser using Cr:YAG as the saturable absorber, the pulse energy at 100 Hz increased from 5.45 to 24.5 μJ when the boundary temperature increased from 26°C to 113°C, while the pulse width decreased by 2.4 times. An improved model based on the rate equations was introduced to analyze the large variation of pulse energy when heating the Nd:YVO4 crystal.