The present invention provides a power module (1) including a substrate (2) and a modular housing structure (3, 3a, 3b, 3c, 3d, 3e, 3f, 3g, 3h, 3i, 3j, 3k, 3m, 3n). The substrate (2) includes an electronic element (21) disposed thereon. The modular housing structure (3, 3a, 3b, 3c, 3d, 3e, 3f, 3g, 3h, 3i, 3j, 3k, 3m, 3n) is disposed on the substrate (2) and located around the electronic element (21). The modular housing structure (3, 3a, 3b, 3c, 3d, 3e, 3f, 3g, 3h, 3i, 3j, 3k, 3m, 3n) includes a plurality of sidewalls (31, 32, 35, 36) configured to connect with each other detachably. Each sidewall (31, 32, 35, 36) includes two connecting elements (311, 312, 321, 322, 351, 352, 361, 362) disposed on two opposite ends thereof respectively. The two connecting elements (311, 312, 321, 322, 351, 352, 361, 362) of any one of the sidewalls (31, 32, 35, 36) are connected to two corresponding connecting elements (311, 312, 321, 322, 351, 352, 361, 362) of two adjacent sidewalls (31, 32, 35, 36) respectively. Consequently, the numbers and connections of the sidewalls (31, 32, 35, 36) are adjustable and varied according to the size of the substrate (2) so as to avoid the waste of space and enhance the power density.