The invention discloses a preparation method for carbon extraction and manganese consercation in medium-manganese low-silicon high-phosphorus molten steel (Mn is 0.70-0.90wt%, Si is 0.06-0.15wt%, P is0.130-0.220wt% and S is less than or equal to 0.045wt%) in converter steel making. By adopting the preparation method, processes such as slag retention operation, continuous casting slag application,little slag smelting, constant pressure gun conversion operation in the smelting process, lowest gun position pressing operation in primary pouring of a converter, and slag wash of whole-process steel discharge, are integrated and created, low-silicon molten steel smelting slagging elements and heat sources are increased, rapid slag formation in the smelting process is promoted, smelting reactionkinetic and thermodynamic conditions are improved, excellent slugging and phosphorus removal effects are achieved, molten steel and slag splashing in the smelting process is avoided, a MnO allocationconcentration is effectively increased, reduction of the MnO at the medium stage of smelting is promoted, secondary oxidation of Mn in molten steel at the later smelting stage is reduced, furthermore, the content of residual Mn in the molten steel at a final point is remarkably increased (0.25-0.38wt%), the addition amount of a manganese alloy in a deoxidation alloying process is reduced, the steel making alloy consumption and alloying cost can be remarkably reduced, and the market competitiveness of products can be improved.