A power assembly with a liquid cooling radiator, a motor control unit, a powertrain, and a vehicle. The power assembly includes a substrate, the liquid cooling radiator, and a sealing member. The substrate is configured to fasten a power switching transistor. The liquid cooling radiator includes a groove structure. The groove structure includes a bottom plate and a side plate, and the bottom plate and the substrate are spaced apart in a thickness direction of the substrate. The sealing member is configured to fasten a peripheral side surface of the substrate and an end face that is of the side plate and that faces away from the bottom plate. A material of the sealing member is different from that of the substrate. The side plate and the substrate are connected through the sealing member, so that connection stability between the substrate and the side plate is improved.