This paper presents size optimization of a carbide anvil based on thermodynamic coupling analysis. In our method, the established carbide anvil assembly through SolidWorks is firstly imported into the finite element software. Then, the temperature field and thermal-mechanical coupling field of the carbide anvil assembly of the diamond press were analyzed. From the simulation results, it can be found that the contact stress of steel ring under temperature load increases by 17.9% compared with that without temperature load. Thus the service life of carbide anvil under temperature load is lower than that without temperature load. It is consistent with the actual crack position of the carbide anvil, which proves the accuracy and effectiveness of thermal-mechanical coupling simulation. The optimization results show that the optimum effect is best when the thickness of carbide anvil is 1.895 cm, the face of carbide anvil width is 16.452 cm, and the height of anvil is 21.03 cm.