The rail is the main component of railway track. Its function is to guide the wheels of the locomotive, bear the great pressure of the wheel, and pass it on to the sleeper. The rail must provide continuous, smooth and minimum rolling surfaces for the wheels. In electrified railway or automatic block section, rail can also be used as an orbital circuit. The type of rail is indicated by the approximate quality of each metre. At present, the rail type of railway in China mainly includes 75kg/m, 60kg/m, 50kg/m and 43kg/m. The world's heaviest rail rail has reached 77.5 kg/m, and our country is also gradually laying 75kg/m rails on overloaded lines. The standard length of rail is 12.5 m and 25m.