In order to improve harmonic conversion efficiency and eliminate walk-off effect,temperature field of nonlinear crystal was accurately calculated. Through work state analysis of KTP crystal with intracavity doubling frequency,a thermal model of rectangle nonlinear crystal was buildt and the radiation eccentricity (RE) of a rectangle crystal was first defined. Based on heat conductive equation,a general analytical solution of temperature model was obtained and the temperature model influenced by eccentric radiated of fundamental wave was first investigated