A numerical calculation model of laser light field considering thermal distribution and gain distribution was constructed to evaluate the beam pointing angle instability of high-power solid-state lasers. The influence of the detuning degree of the resonant cavity output mirror and the mirror on the beam pointing stability was analyzed. The cavity mirror rotation perturbation factor and the cavity mirror movement perturbation factor were defined to describe the degree of parallel detuning and coaxial detuning of the cavity mirror, respectively, and the perturbation factor, thermal effect modulation and gain modulation were introduced in the calculation of the resonant cavity light field. The influence of resonant cavity parameters on the beam pointing stability of high-power Nd:YAG solid-state laser under the condition of cavity mirror detuning was studied. When the pump power is 10 000 W, and the cavity mirror rotation perturbation factor and the cavity mirror movement perturbation factor changing 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 laser beam pointing offset angle in the pump pulse time is 1×10^?6 rad~5×10^?3 rad.