The invention discloses a DC-DC converter sliding mode controller based on a power constant-speed reaching law. The sliding mode controller is arranged in a BUCK converter, and is connected with a power supply, an inductive current collector and a switching device. The DC-DC converter sliding mode controller comprises a model construction module, of which the first input end is connected with thepower supply and the second input end is connected with the inductive current collector; a calculation module, of which the first input end is connected with the output end of the model construction module; a detection module, of which the input end is connected with the output end of the calculation module, and the first output end is connected with the second input end of the calculation module;and a control module, of which the input end is connected with the second output end of the detection module, and the output end is connected with the switching device. According to the method, the problem of serious buffeting phenomenon of output control of a sliding mode variable structure in a DC-DC converter is solved, composite control of the sliding mode variable structure under the actionof time-varying disturbance is realized, and the control precision and the anti-interference performance of the sliding mode variable structure are improved.