Piston ring is the core component of fuel engine. The sealing of fuel body and cylinder, piston and cylinder wall has been completed by it. The piston ring includes four functions: sealing, regulating oil (oil control), heat conduction (heat transfer) and guidance (support). Sealing: refers to the sealing of gases, so as to avoid the leakage of combustion chamber gases into the crankcase, to minimize the leakage of gases and improve thermal efficiency. Leakage not only reduces engine power, but also deteriorates the oil, which is the main task of the gas ring; oil regulation (oil control): scrape the excess lubricant from the cylinder wall, while making the cylinder wall covered with film, to ensure the normal lubrication of the cylinder, piston and piston ring, which is the main task of the oil ring. In modern high-speed engines, the role of piston rings in controlling oil film has received special attention; heat conduction: through the piston rings, the heat of piston is transferred to the cylinder liner to play a cooling role. According to reliable data, 70-80% of the heat received by the top of the piston in uncooled piston dissipates to the cylinder wall through the piston ring, 30-40% of the cooling piston dissipates to the cylinder wall through the piston ring; support: the piston ring keeps the piston in the cylinder, prevents the piston from contacting directly with the cylinder wall, ensures the smooth movement of the piston, reduces friction resistance and prevents the piston from moving. Poor accuracy of piston ring material will damage the guiding (supporting) function.