Abstract: According to the basic theoretical formula of two-film theory, we derive the calculation formula of oxygen content change in the offshore platform water injection system after air-water backwash. On the basis of the calculation formula, the effects of different backwash methods on the oxygen content in the process are analyzed, and the influence of the water injection process in a certain offshore oilfield on the oxygen content of the process is analyzed. Analysis results show that the air-water alternative backwash mode in offshore platform will not lead the oxygen content change to exceed the limit for injection water defined in related standards.