The invention discloses a relaxation power positioning control system based on model prediction control. The relaxation power positioning control system comprises a sensor module, an extended Kalman filter, a nautical chart calculation unit, an environmental disturbance compensator, a controller and a marine power plant. The sensor module comprises a position reference system and a compass and sends north coordinate information x, east coordinate information y and course information psi to the extended Kalman filter. The extended Kalman filter estimates state estimation information of the system, the nautical chart calculation unit generates state expected information, the environmental disturbance compensator acquires and sends environmental disturbance to the controller, the controller comprises an optimizer and a nonlinear model prediction controller, the optimizer generates an optimal initial control value and sends the optimal initial control value to a nonlinear model predictor, and the nonlinear model predictor generates control instructions and sends the control instructions to the marine power plant. Control signals generated by the relaxation power positioning system slowly change, it is optimal in the energy aspect, and energy consumption and abrasion of a propulsion unit are effectively reduced.