Tractor is a self-propelled power machine used to pull and drive the working machinery to complete various mobile operations. It can also be used as fixed operation power. It is composed of engine, transmission, walking, steering, hydraulic suspension, power output, electrical instruments, driving control and traction systems or devices. The power of the engine is transmitted from the transmission system to the driving wheel, which makes the tractor drive. In real life, the rubber belt is often used as the power transmission medium. Tractors can be divided into agricultural, industrial and special-purpose tractors according to their functions and uses; tractors can be divided into wheel type, crawler type, ship type and self-propelled chassis according to their structural types.