Boiler feed water firstly flows into the water chamber of deaerator. Due to certain pressure drop, water is sprayed into film spraying pipe through water inlet port, and then the water rotationally flows forward along the internal wall of the spraying pipe. The flowing water forms rotating waterfilm skirt at the outlet of film-rotating pipe. The interior and exterior surfaces of the water film skirt fully contact with the heated steam, and the water is heated to the saturated temperature instantly. Most of the non-condensable gases are separated out. On this rotating-film deaerating stage about 90% of oxygen is preliminarily removed.