The invention discloses high-power mechanical speed changer active-lubricating device and method. The device comprises a gear pump, a main oil circuit and a branch oil circuit. The method comprises the following steps of building a thermodynamics simulation analysis model of a main transmission part, calculating loading and stressing conditions of a gear and a bearing under the design condition, calculating the heat production quantity of each heat production point and the total heat, calculating the flow demand of a corresponding lubricating system under the heat balance temperature, calculating the heat balance flow demand corresponding to each lubricating point and the total flow demand, obtaining the flow distributed for each lubricating point under the highest speed working condition,building a hydraulic simulation analysis model, comparing the simulation flow of each lubricating point and the flow required for heat balance, and enabling the flow distributed for each lubricatingpoint to be close to the flow required for heat balance through changing an oil channel and increasing the local damping. The invention aims to provide the high-power mechanical speed changer active-lubricating device and the design method which can meet the actual use requirement of a high-power mechanical speed changer.