The present disclosure provides a power battery pack, including: a battery pack case, at least one battery module, and a return pipe. An oil inlet and an oil outlet are formed on the battery pack case, and insulation oil is charged from the oil inlet into the battery pack case. Each of the at least one battery module is disposed in the battery pack case, and each battery module includes a module case and at least one unit cell disposed in the module case. The unit cell is immersed in the insulation oil, and the bottom of the module case is provided with a through hole and the top of the module case is provided with at least one exhaust vent. The return pipe is disposed outside the battery pack case, and the return pipe is connected between the oil outlet and the oil inlet.