The invention discloses a power optimization control method for a power unit of a multi-shaft heavy-duty hybrid power vehicle. The method comprises the steps that a power point of the power unit is calibrated with reference to an engine external characteristic curve at full range rotating speed, and an optimum working area of engine discretization is determined; the power unit receives a target output power instruction in real time and determines the actual target power when the engine enters a power generation state; according to the current output power and the actual target power of the engine, the power unit follows the principle of minimizing the rotating speed adjustment, determines the target working point in the optimum working area, and switching is carried out to complete the power switching control of the engine. The power optimization control method for the power unit of the multi-shaft heavy-duty hybrid power vehicle adopts the control method of rotating speed/torque, so that the working point of the power unit is always in the optimum working area, and the rapidity of power output response is taken into account so as to realize the improvement of response speed and fuel economy.