A trailer is a vehicle that is pulled by a car and has no power drive itself. It consists of a combination of a car (truck or tractor, forklift) and one or more trailers. The truck and the tractor are the driving car section of the car train, called the main car; A driven car segment pulled by the main car is called a trailer. Trailers are divided into full trailers and semi-trailers according to the connection between the trailer and the tractor. A trailer that is pulled by a tractor and whose entire mass is borne by itself; A trailer that is pulled by a tractor and part of its mass is borne by the tractor. It has the advantages of speed, mobility, flexibility, safety, etc., and can conveniently realize section transportation.