In order to clarify the effect of mixed lubrication methods on the oil flow and power loss of the gearbox, this study adopts a high-precision moving particle semi-implicit (MPS) method to investigate the lubrication of the gearbox under the joint influence of splash lubrication and oil injection lubrication. The accuracy of the numerical method to calculate the churning torque was verified by the constructed test rig. The effects of rotational speed, immersion depth, injection volume rate, and oil injection angle were analyzed and evaluated for lubrication. The results show that better lubrication can be achieved with relatively small churning torques by using a hybrid lubrication method. This provides some references for engineering applications of gearboxes.