The expression for the temperature distribution in the end-pumped slab cross section was deduced and the thermal distortions in single and composite medium were analyzed. The results indicate great difference in temperature distribution and thermal distortion exists between composite and single slabs. For the single slab,positive lens caused by thermal gradient could be reduced by increasing the bounce number of the light in zigzag propagation through the slab. For the composite slab,the thermal lens may be positive or negative. Thus the thermal distortion could be reduced either by increasing the bounce number of the light in zigzag propagation through the slab or by optimizing the length of each segment at the given bounce number.