Thermal stress simulation and optimization design of the parameters were performed for the W/Cu FGM of divertors by finite element ANSYS code. The results show that the thermal stress is decreased greatly by the introduction of the W/Cu FGM, and the maximum von mises stress is decreased approximately by 58%. The optimal parameters of the FGM are as following: the layer number of FGM is about 5 and the distribution exponential of Cu volume content is about 0.4. Meantime a good heat resistance is shown with a surface temperature below 800 oC under the 10 MW/m2 surface heat load