Abstract: In order to study the thermal effect of Yb∶YAG crystal endpumped by pulse laser diode(LD),the temperature distribution of crystal was calculated based on semianalytic method. The crystal thermal model was built under the real work situation and the initial conditions and boundary conditions were established in this research, according to the working characteristic of square Yb∶YAG micro crystal endpumped continuously by LD. Furthermore, considering the function relation between the coefficient of thermal conductivity and temperature and solving the heat conduction equation with Newton method, the temperature distribution was obtained. Finally, the influences of different factors such as the different pump power, super Gauss order, radius of spot, thickness of crystal on crystal were studied. The research results show that maximum temperature of Yb∶YAG crystal endpumped surface is 41.25 ℃ and 52.14 ℃,respectively, under the different conditions that thermalconductivity is constant and nonconstant. And in that case, the first order superGaussian light was used,with the output power of 80 W and the spot radius of 400 m, to pump the crystal with the mass fraction of 8% and the size of 431 mm3. It is very significant to reduce the thermal effect of full solid state Yb∶YAG crystal in this research.