An assembly mechanism is provided to press an inner stator into a receiving space of an outer stator. The assembly mechanism includes a pressing unit and a first positioning plate. The pressing unit includes a supporting device to support the outer stator, and a pressing device movable relatively to the supporting device. The first positioning plate is attached to a top of the outer stator. The first positioning plate defines an opening forming a clearance fit with the inner stator. The opening receives the inner stator and guides the inner stator to move into the receiving space of the outer stator under a pressing action of the pressing device. An assembly method is also provided.