The steady-state temperature distribution of high-power semiconductor lasers is simulated, the thermal lens focal length and the variation of the slow axis divergence angle are calculated with the temperature distribution under different thermal power conditions. Results show that, under the same conditions the thermal power and the thermal lens focal length are approximately inversely proportional, and the slow axis divergence angle is approximately linear with thermal power. When the thermal power reaches 10 W, the thermal lens focal length is 568 μm, and the slow axis divergence angle increases about 10°. The slow axis divergence angle of the laser under different working current conditions is measured and the results show that the simulated values are consistent with the experimental values.