Under the influence of thermal effect, how to optimize the conversion efficiency of laser diode (LD) end-pumped solid-state lasers is analyzed. Considering the effect of pump beam distribution, the laser medium and the resonator structure, a simulation algorithm is designed to calculate the thermal effects and laser conversion efficiency. The results show that thermally induced loss is relevant to pump radius, pump power, cavity length, oscillation light radius and crystal materials. It is independent of output mirror transmission and repetition rate. Considering the existence of thermally induced loss, there are optimum pump parameters and resonator parameters which make the conversion efficiency of NdYAG largest when pump power is fixed.