A stator assembly is used to be assembled to form a stator core. The stator assembly includes a tooth and a yoke. One end of the tooth is connected to the yoke. The yoke has an inner side, an outer side, a first coupling side, and a second coupling side. The first coupling side further includes a first engaging structure, and the second coupling side further includes a second engaging structure. The second engaging structure corresponds the first engaging structure. The outer side has a groove. The groove has a side surface and a bottom surface. An angle is defined between the side surface and the bottom surface, and the angle is in a range from 135° to 165°.