The theoretical simulation and experimental study on thermal effect of bounce-pumped slab amplifier is presented. Based on an efficient cooling of conductively cooled, the temperature distribution of the slab is calculated by finite element analysis, and the beam quality is calculated by the method of moments, which gives a guide for the thermal compensation. The focal length is obtained experimentally and the experimental results agree with the theoretical analysis well. When the three-stage amplifier is operated at the repetition frequency of 250 Hz, with a designed thermal compensation lens, an output laser whose pulse energy is 537 mJ and the beam quality factor M2x=2.35, M2y=2.66, is obtained.