Assembly part of valve, automobile and rear axle brake system of automobile

The invention provides an assembly part of a valve. The valve comprises a first valve body and a second valve body. The assembly part of the valve comprises a nut base, a through joint and a positioning piece, wherein the nut base is used for being matched with internal threads of the first valve body and connected with the first valve body in a sealing mode, the through joint is used for being matched with the second valve body in a threaded mode and arranged at the head end of the assembly part, a clamping groove is formed in the tail end of the through joint, the through joint is arranged in the nut base in a sleeved mode and connected with the nut base in a sealing mode, and the positioning piece is connected with the nut base, used for positioning the through joint, and matched with the clamping groove. According to the assembly part of the valve, due to the adoption of the through joint, the nut base and the positioning piece, connection between the first valve body and the second valve body is achieved, the distance between the first valve body and the second valve body is shortened, and thus space occupied by a system with two or more connected valves is reduced. The invention further provides a rear axle brake system and an automobile.