The invention relates to a power module comprising a substrate and a cordwood system shell. The substrate comprises at least one electronic component. The cordwood system shell is arranged on the substrate and surrounds the electronic components. The cordwood system shell comprises multiple retaining walls which are detachably assembled, and each retaining wall is provided with two connecting components which are arranged at the two side edges of the retaining wall, wherein two connecting components of any retaining wall are assembled with the corresponding connecting components of the adjacent retaining wall. The number and the combination mode of the retaining walls of the cordwood system shell can be changed according to the size of the substrate so that the production cost of the power module can be reduced and the power density can be enhanced.