The invention provides a gaseous polymerization system and a nozzle device thereof, the nozzle device comprises a nozzle body and an ejecting hole that stretches along the axial direction of the nozzle body, the nozzle device also comprises a catalyst feed opening and a first gas access hole which are communicated with the ejecting hole, the nozzle device also comprises a second gas access hole, the outlet of the catalyst feed opening and the outlet of the first gas access hole are communicated with a feed port of the ejecting hole, and the outlet of the second gas access hole is arranged at the outlet end of the nozzle body. The nozzle device in the invention comprises the second gas access hole, the outlet of the second gas access hole is arranged at the outlet end of the nozzle body, the second gas access hole can blow the material ejected from the interior of the ejecting hole, not only can the atomization effect be enhanced, but also the problem that the outlet of the nozzle device is obstructed can be eliminated thoroughly, and the long-period and unremitting feed of slurry catalyst can be maintained.