Thermal distortion is a key problem for solid-state laser design. In this paper, with the help of finite element analysis software, the steady-state and transient temperature and stress distributions of Yb∶YAG with active-mirror structure were analyzed and compared under different pumping light characteristics and cooling conditions. The results show that the uniformity of the pump light has great influence on the temperature gradient in the laser crystal. In addition, the peak value of the transient temperature gradient is larger than that of the steady temperature gradient under the same pumping and cooling conditions.