Abstract: The tungsten monoblock of divertor in nuclear reactor cracks and fails as a result of high temperature and thermal stress under the working condition of high heat flux. The effects of self-developed W-diamond composites with different thermal conductivities on the temperature and thermal stress of the tungsten monoblock of divertor were investigated.Firstly, the theoretical physical properties of W-diamond composites at different temperatures were calculated by theoretical formulas. The thermal stress and temperature distribution of tungsten monoblock with W-diamond composites with different thermal conductivities and pure tungsten material as plasma-facing materials(PFM)at 20 MW/m² heat flux were simulated and compared by ANSYS software.The result shows that, using W-diamond composite as PFM can greatly reduce the maximum module surface temperature, improve the module temperature gradient, reduce the effects of modules. However, due to high elastic modulus of the composite material, the effective stress of the module is not relieved. The result can provide important technical support for the design of W-diamond composite and structure optimization of divertor.