A three-dimensional thermo-elasto-optical distortion model for the laser disk has been constructed, the temperature and stress distributions under different work conditions on a laser disk of a heat capacity laser have been simulated by using ANSYS software, and the effect of the stress on the beam quality with nonuniform pump has been analyzed. An demonstration experiment is done, and the results are accordant to the simulation results. The results show that at the heat capacity mode, the thermal induced birefringence is the main reason to affect the output beam properties.