A three-dimensional object forming apparatus for forming a three-dimensional object includes: a base platform; a transmission portion; a detachable construction tank; a movable powder supplying tank provided for driving to supply construction powder above the detachable construction tank; a print module including at least a print cartridge with at least a nozzle; a heating portion; an lifting portion arranged below the detachable construction tank; a nozzle cleaning module; a nozzle sealing module having a holder, at least a sealing portion and a moisture portion; and a stretchable dust-proof cover connected to a side of the powder supplying tank, which is provided for moving together with the powder supplying tank to cover the construction powder in the construction tank.