The all volatile treatment (oxidation)(AVT(O)) instead of all volatile treatment(reduction) (AVT(R)) has been applied to 600 MW once-through supercritical units with high deposition rate, where the iron content decreases at the economizer inlet, no obvious increase of pressure drops is found at the feedwater pumps and control stage of turbines, and the safe operation of the units is improved. The selection and characteristics of the feed water treatments are analyzed. In addition, the control conditions and iron content determination methods are discussed based on AVT(O) method. It is concluded that AVT(O) can be applied instead of AVT(R) for supercritical once-through units with high deposition rate when oxygenated treatment(OT) is not qualified.