The utility model discloses a vehicle braking variable-pressure regulating device, which comprises an upper cover, a shell, a piston and a membrane. The upper end of the shell is screwed with the upper cover; the two ends of the shell is provided with an upper cavity and a lower cavity; the upper cover and the shell is respectively provided with an air inlet which is communicated with the upper cavity; the lower cavity is in ladder shape; the piston is arranged in the lower cavity of the shell, the upper linkage rod is screwed with the membrane arranged in the upper cavity and the lower linkage rod is screwed with the membrane arranged in the lower cavity; the positions of the shell opposite to the upper plane and the lower plane of the piston are respectively provided with two air inlets, which are communicated with the lower cavity and divide the lower cavity into two working chambers. Through the connection between the lower end of the shell and various trailer valves, relay valves or general braking pumps, the utility model regulates the braking force of empty vehicles, full vehicles, overload vehicles and different road conditions. The regulating device divides the pressure entering into the braking chamber into six levels with two levels for pressure decrease, three levels for pressure increase and one level for balance. With the advantages of balanced braking, difficult locking, quick speed reduction, and less tire wear, the utility model with double membranes reduces the fricative resistance of the piston and ensures that the piston can easily reset and the work becomes flexible.