Piston is a reciprocating movement in the cylinder body of an automobile engine. The basic structure of the piston can be divided into top, head and skirt. The top of the piston is the main part of the combustion chamber, and its shape is related to the selected combustion chamber form. Gasoline engines mostly use flat top piston, which has the advantage of small heat absorption area. Diesel engine piston top often has a variety of pits, its specific shape, position and size must be with the diesel engine mixture formation and combustion requirements.