The invention relates to a converter steelmaking method through power injection dephosphorization by adopting a supersonic speed oxygen lance and a supersonic speed oxygen lance, which can be used for solving the problems that slagging is slow in the steelmaking process and the dephosphorization rate is low caused by low stirring intensity in a dephosphorization period. A slagging material used for dephosphorization is transmitted through a supersonic speed oxygen lance and is sprayed into a molten pool in a supersonic speed power gas jet flow state and is fully contacted, so that rapid slagging is realized in the steelmaking process; thermodynamic and dynamic conditions of dephosphorization reaction are improved; and the steelmaking dephosphorization rate is improved; a power feeding pipe of the supersonic speed oxygen lance is connected with a oxygen blowing central pipe; the outlet of a power supply pipe is positioned between the upper part of the oxygen lance and the outlet of a sprayer; the inner diameter is 10-150mm; the power injection flow is 30-500kg/min; the carrier gas flow is 50-3000Nm3/h and the pressure is 0.4-1.4MPa; a wear-resistant material is adopted at the damage part of a lance sprayer; and the mach number is 1.5-2.1. The converter steelmaking method is suitable for30-350 tons of a converter steelmaking dephosphorization process; compared with the traditional steelmaking process, the dephosphorization rate using the method can be improved by over 5%; the consumption amount of the slagging material is lowered by over 10%; and the metal yield is improved by over 0.5%.