A package structure of a power module includes an insulation frame, a first circuit substrate, an insulation cover, plural first pins, plural posts and a fastening element. The insulation frame includes a sidewall and a first coupling part. The first coupling part is externally protruded from the sidewall. The first coupling part includes a first mounting structure. The first circuit substrate is combined with a bottom part of the insulation frame. The insulation cover is combined with a top part of the insulation frame. The insulation cover includes a second coupling part. The second coupling part includes a second mounting structure. The plural posts are embedded in the at least one first coupling part of the insulation frame, and partially penetrated through the second coupling part. The fastening element is connected with the first mounting structure and the second mounting structure.