Abstract: In microwave plasma CVD equipment,the inhomogeneous distribution of microwave electromagnetic field results in the inhomogeneous temperature of the plasma ball and substrate,and lowering quality of CVD diamond,so it is necessary to heat the substrate.Material's absorbability to microwave energy relates with microwave frequency,electric field intensity,material's dielectric constant,dielectric loss and material's volume.It is a function that temperature to material's dielectric constant and loss and thermal conductivity and so on. Based on thermodynamic theory, this paper researched the three-dimensional axialsymmetric temperature field model,in which above parameters were changed with temperature to heating substrate material, obtained analytic expression of temperature distribution, used silicon carbon material which can absorb microwave energy powerfully, and used it as material of heating substrate and laid it down in the substrate in the microwave plasma cavity.The calculated results show that the model can come into homogeneous temperature distribution,which has φ76.2mm diameter and temperature change is only less 10℃,so it is very useful to heat the substrate.