The formation mechanism and protection performance are introduced of the passive film formed by oxgenated treatment of boiler feedwater. A series of experiments about the protection performance of the passive film are conducted after oxygenated treatment of boiler feedwater is ceased in 1000 MW ultra-supercritical units. It is shown that the passive film is also protective for a long period. Furthermore, it is feasible for the boiler feedwater to be discontinuously oxygenated.