The thermodynamics of electro-optic switch materials such as LiNbO3, DKDP and KDP used in high average power laser systems is analyzed by use of finite element methods. The results show that when the power of input laser with the facular of 20 mm×20 mm gets up to 2 kW under the radiation time of 10 s, the maximum temperature rises of the three materials are 0.45 K, 7.04 K and 76.02 K, respectively, and the maximum thermal stresses are 0.528 MPa, 4.78 MPa, 47 MPa, respectively.