By using the matrix theory of the laser resonators, the G parameters of plane-plane cavity and the condition of themal thick len inside laser resonators are given. The optimistic design of laser resonator is made to obtain by using the graphic method Then the experiments are carried out with the designed resonators parameters.When input electric power is 450W, its output laser power is up to 50W, The electro-optic efficiency is 11.1% and the light to light conversion efficiency is up to 30%. The power stability is ±2 %。