In order to obtain simple and compact solid-state lasers,a LD end-pumped slab laser with a folded three-pass resonator was used and its thermal lens equivalent cavity model was established. The equivalent cavity stability and cavity mode radius were simulated and analyzed. The new structure and flat cavity structure were studied comparatively based on experiments.The results show that,when the length of the folded three-pass cavity is 170 mm,the power output of 1064 nm laser is 21 W,lightlight efficiency is...