The solid state laser resonance cavity with thermal lens is analyzed, the G parameters of resonance cavity are obtained, changing G parameters with the pumped power are analyzed and discussed, and the changes of output power of the different cavity are presented. By studying the Tm:YAP laser, the changes of output power of different cavity are validated by the experimental results. To the plane-plane cavity solid state laser, a conclusion that short cavity is appropriate for high power output is obtained.