Thermal stress and optimum structure design of tungsten/copper functional gradient materials (W/Cu FGM) were analyzed via ANSYS12.0 code. The results show that the maximum thermal stresses firstly decrease to a bottom value and then slightly increase with the increasing of compositional exponent (p) of W/Cu FGM. The equivalent Von Mises thermal stress for the W/Cu FGM (p=1.3) is 180 MPa, decreased by 79% compared with non-FGM under heat flux of 30 MW/m2. According to the simulation results, the optimal parameters of the W/Cu FGM are listed as following: above 3 mm for the thickness, 4~6 layer for the W/Cu FGM and 1 mm to 3 mm of the thickness for the tungsten layer.