The influence of laser resonator misalignment on laser performance was investigated theoretically and experimentally. In theory, based on the character of quasi-continuous diode-pumped electro-optical Q-switched solid-state laser, the rate equation model including the modifying function of cavity misalignment was set up. The influence of cavity misalignment on laser losses and laser performance was simulated with different laser modes, laser beam radius, radius of iris and position of iris and the influence of cavity misalignment on laser performance was simulated by model′s numerical simulation. On the other hand, the influence of resonator misalignment on laser performance was measured in experiment. For the concave-convex cavity with cavity length of 250 mm and iris radius of 3.5 mm, the influence of concave mirror′s misalignment on laser performance was more serious than that of the convex mirror′s misalignment. The energy decreased from 220 mJ to 150.9 mJ corresponding to decreasing of 31.4% and pulse width increased from 5 ns to 6.5 ns with the concave mirror′s misalignment angle increasing from 0 to 490 μrad. The experimental results and theoretical results are in good agreement, indicating the validity of the laser model. The established laser model and the utilized experimental measuring method can be effective means to obtain the influence of resonator′s misalignment on laser performance, which can be a reference of the design of high reliability laser.