Prefabricated balconies are divided into overlapping balconies (semi-prefabricated) and fully prefabricated balconies. The surface smoothness of the fully prefabricated balcony can be as flat as the surface of the die or be made into a depression. The slope of the ground and the drainage outlet are also prefabricated in the factory. Prefabricated balconies can save on site moulding and expensive support. In the composite slab system, the prefabricated balcony, the composite floor and the composite wallboard can be poured into a whole at one time.