Abstract: The thermal distortion in the conduction cooled end-pumped zig-zag slab under different cooling conditions were analyzed by numerical simulation. The results indicate that the thermal distortion could be reduced by 3 orders of magnitude in zig-zag propagation. The inversion phenomenon of wave front was observed when different zig-zag optical paths were selected. The zig-zag optical path can eliminate the influence of the non-uniform heat dissipating capacity in length and height directions, but not in width direction. When the heat dissipating capacity in slab’s width direction is non-uniform, the thermal distortion increases significantly and the propagation direction will be deviated．Therefore, when the heat dissipating capacity of the slab is non-uniform, small bounce number of zig-za