The invention discloses a brake adjuster. The brake adjuster comprises a right assembly, a left assembly, an adjusting nut and a screw assembly, wherein the adjusting nut is arranged in the right assembly and is connected with the screw assembly in a threaded manner. A compression spring is sleeved with the adjusting nut and between the adjusting nut and the right assembly, the lower end of the screw assembly is disposed in the left assembly, the lower end of the screw assembly forms a driving protrusion along the radial direction, one side of the driving protrusion is abutted against one end of a graduating stem, and the other side of the driving protrusion is abutted against a conical spring in the left assembly. The screw assembly is connected with a one-way bearing, and the upper end of the screw assembly is connected with a retreat nut. A gap between a brake disc and a brake pad is self-adaptively adjusted when enlarged after wear of the brake pad of a railway locomotive, so that the gap can meet the normal requirements of design; after brake is alleviated, adjustment of the gap can be kept, so as to meet the brake requirements of the next brake.