A bearing retaining structure includes a base, a stator assembly and a bearing. The base has a bearing cup projected from one side thereof, and the bearing cup internally defines a receiving space and has a fixed end connected to the base and an opposite free end. The bearing is disposed in the receiving space of the bearing cup. The stator assembly has an axially extended central opening and a retaining portion radially inward protruded from an inner wall surface of the central opening. The stator assembly is externally mounted around the bearing cup with the retaining portion tightly fitted around the free end of the bearing cup to narrow the receiving space, so that an inner wall surface of the receiving space is in tight contact with an outer wall surface of the bearing, and the bearing is stably retained in the bearing cup.