CFD analysis was carried out on the in-cylinder and water jacket with AVL-Fire. In order to achieve the conjugate heat transfer, the convection thermal boundary conditions were coupled to the calculation process of the solid heat conduction with FE technology. The calculation of the cylinder head stress under the mechanical and thermal load was done. Finally, the mechanical-thermal fatigue integrating the material properties corrected by temperature, and the access to the safe factor, were analyzed. The results have shown that, in terms of the fatigue of cylinder head, the contribution of thermal load is noticeably greater than the mechanical load. The results have also shown that the cylinder head design meets its work demand.