A converter oxygen blowing method capable of blowing oxygen by using upward blowing lance having a De Laval Nozzle fitted to the tip thereof, wherein the De Laval Nozzle comprises a nozzle back pressure P0 (kPa) meeting the requirement of an expression P0=Fhs/(0.00465.Dt ), where an acid feed rate for each rubber nozzle hole determined by the acid feed rate Fs (Nm /hr) in the high carbon area of a peak decarbonizing period is Fhs (Nm /hr) and a throat diameter is Dt (mm), and the outlet diameter (De) of the De Laval Nozzle meets the requirement of the expression De = 0.23 x Dt /{(Pe/P0) x [1-(Pe/P0) ] }, where a nozzle back pressure is P0 (kPa), atmospheric pressure is Pe (kPa), and the throat diameter is Dt (mm).