Abstract: The 00Cr13Ni4Mo ultra low-carbon martensitic stainless steel was decarbonization refined by a 40t VOD.The vacuum degree,temperature,supplying oxygen intensity,and argon intensity were controlled as about 260660 Pa, 1600℃, 570 Nm³·h^-1, and 48.4 NL³· min^-1, respectively,during inputting oxygen by regulating the optimal parameters in the furnace.However,after finishing blowing oxygen,these four parameters changed to 7998 Pa, 1750 to 1800℃, 550 Nm³·h^-1,and 117.5NL³· min^-1, respectively.The height of oxygen lance was controlled as 75mm.It should be pointed that the increase of supplying argon intensity at the same stage can expedite the circular speed of molten steel in the ladle.