The invention provides a fabricated building externally-hung protection device comprising a protection frame with a plurality of transverse rods and a plurality of vertical rods. The protection frameis internally provided with a protection net and/or a guard bar, the externally-hung protection device further comprises a plurality of fastening devices pre-buried at the outer ends of prefabricatedoverhung components and a plurality of hook seats fixedly connected with the fastening devices through fastening pieces, and the protection frame is provided with hanging rods protruding towards the prefabricated overhung components. The hanging rods are closer than the prefabricated overhung components compared with the protection net and/or the guard bar, and the protection frame is hung into the hook seats through the hanging rods. According to the fabricated building externally-hung protection device, the weight of the externally-hung type protection net is greatly reduced, the load of theoverhung components such as a balcony and a bay window is reduced, the structural safety of the balcony and the bay window is ensured, meanwhile the current condition that the load is concentrated toa construction platform is further improved, and the stability of the externally-hung type protection net is improved.