To promote the deoxygenization efficiency of modified sponge iron deaerator, the deoxygenization mechanism was studied with the aid of kinetics and characterized analysis. The application of modified sponge iron deaerator for high pressure boiler feed water was investigated as well. The results showed that the process of deoxygenization was a first order reaction regarding for active sites decay. The modified sponge iron was able to reduce dissolved oxygen (DO) level from ppm levels down to a few ppb levels and the dissolved iron in outlet can be removed completely by ion exchange resin. Therefore, the application of modified sponge iron deaerator for high pressure boiler feed water was feasible.