Abstract: A numerical calculation model of laser light field considering thermal distribution and gain distribution is constructed to evaluate the beam pointing angle instability of high-power solid-state lasers. The influence of the detuning degree of the resonator output mirror and the mirror on the beam pointing stability is analyzed. The cavity mirror rotation perturbation factor and the cavity mirror moving perturbation factor are defined to describe the degree of parallel detuning and coaxial detuning of the cavity mirror, respectively. The perturbation factor, thermal effect modulation and gain modulation are introduced in the calculation of the cavity light field. Using this method, the influence of resonator parameters on the beam pointing stability of high-power Nd : YAG solid-state laser under the condition of cavity mirror detuning is studied. When the pump power is 10000 W, when the cavity mirror rotation perturbation factor and the cavity mirror movement perturbation factor change in the range of 1×10⁻⁴~50×10⁻⁴ and 1×10⁻⁷~50×10⁻⁷, respectively, the fluctuation range of the root mean square value of the laser beam pointing offset angle in the pump pulse time is 1×10⁻⁶~5×10⁻³ rad.