The present disclosure provides a power module, a power module assembly and an assembling method thereof. The power module assembly includes a housing, a resilient bracket, a circuit board, a power device and a fastening unit. The housing includes a first heat-dissipation surface. The resilient bracket is pre-fastened on the housing. The resilient bracket is located near the first heat-dissipation surface and configured with the first heat-dissipation surface to form an accommodating space. The circuit board is configured to assemble on the housing. The power device is plugged in the circuit board and accommodated in the accommodating space. The fastening unit is pre-fastened on the housing and pressing the resilient bracket. While the resilient bracket pushes against the power device, the power device is attached to the first heat-dissipation surface.