The cylinder head is installed on the top of the cylinder block, which seals the cylinder from the top and constitutes the combustion chamber. It is often in contact with high temperature and high pressure gas, so it bears a large thermal load and mechanical load. A cooling water jacket is made inside the cylinder head of the water-cooled engine, and the cooling water hole on the lower end face of the cylinder head communicates with the cooling water hole of the cylinder block. Use circulating water to cool high temperature parts such as the combustion chamber.