The function of the cylinder head is to seal the cylinder, form a combustion space with the piston, and bear the function of high temperature and high pressure gas. The cylinder head bears the mechanical load caused by gas force and tightening cylinder bolts. At the same time, it also bears high thermal load due to contact with high-temperature gas. In order to ensure the good sealing of the cylinder, the cylinder head shall not be damaged or deformed. For this purpose, the cylinder head should have sufficient strength and stiffness.