Abstract: Object：By Comparision of the thermal injury effect of Nd:YAP laser with that of pulsed and con continuous wave Nd:YAG laser to get more knowledge of the thermal injury effect of Nd；YAP laser. Method:Wister rats were used in the experiment,they were divided into two groups including skin muscle group and liver vein group. Three kinds of laser was used in the first group, Nd:YAP and Continuous Wave Nd:YAG laser were used in the latter group, both irradiating by uncontacted point irradiation. Energy density 1000 and 2000 J/cm2 , 500 J/cm2 and 1000 J/cm2 were used respectively. The injury was observed by eye during irradiation. The biopsy was taken at the moment, 3 days after irradiation. Histomorphologic changes of the injured tissue and its healing procedure were observed with light microscopy. Results：In skin muscle group, under 2000J/cm2 the main thermal injury effect of Nd:YAP laser is thermal coagulation effects. Under 2000J/cm2 Nd:YAP laser has obvious gasification effect. Under the same energy density, the gasification effect of Nd:YAP laser is significant than that of two Nd:YAG lasers, while the depth of coagulation injury is smaller than that of Continuous Wave Nd:YAG laser and largerer than that of pulsed Nd:YAG laser. In liver group, the gasification effect of Nd:YAP laser is more evident than that of Continuous Wave Nd:YAG laser., although their thermal coagulation effects are resembling. In vein group, the thermal coagulation and gasification effects of Nd:YAP laser is heavier than that of Nd:YAG laser. Conclusion：Nd:YAP laser has both gasification incision and coagulation effects.