Abstract: A carbon-fiber product forming device is disclosed. The device includes a first chamber forming with a hollow cavity, a hot-pressing plate disposed inside the hollow cavity, a mold disposed on the hot-pressing plate and formed with an outward opening, an air bag disposed inside a mold cavity of the mold, provided with a bag opening disposed near the outward opening, and attached on an outer surface thereof with carbon-fiber composites, a second chamber mounted on one side surface of the first chamber and disposed on wall surface with an air extracting port, an air inlet port, a heat medium entry port, and a barometric port, and a plurality of barometric pipes included inside the second chamber. Two ends of each of the barometric pipes are connected to the barometric port and the outward opening, respectively, such that the air bag could be periodically injected with air.