The invention discloses a constant-power steel rail burnishing method. Control units control down force applied to a burnishing motor from a hydraulic system so as to control output power of the burnishing motor, under the control of the hydraulic system, the burnishing motor drives a grindstone to press downwards to a steel rail, and after the grindstone is in contact with the steel rail, the output power of the burnishing motor is changed. The output power of the burnishing motor is fed back to the control units, and the control units realize the purpose that in a moving burnishing process of a steel rail burnishing wagon, the burnishing motor is constant in output power by controlling the down force applied to the burnishing motor from a current regulating hydraulic system of a proportion valve according to a given target power and the output power of the burnishing motor. According to the constant-power steel rail burnishing method disclosed by the invention, the technical problems that for a conventional milling manner, in the burnishing process, small-wavelength wave-shaped milling is easy to form, the rail surface of the burnished steel rail is uneven, and errors of the rail surface cannot be well eliminated, can be solved.