Abstract The thermal conduction theory based on uniform heating in the slab laser has presented before, but the results obtained from this theory disagree considerably from the results of experiment. In this paper, a non-uniform heating model based on the absorption law of medium is proposed. According to this model, the temperature distribution in the slab laser under CW and pulse pumping is solved. Thermal stress and fracture limitation of the slab are given. The new model is in accordance with the experimental results.