Abstract: According to thermodynamic calculation it is obtained that by BOF double slag method in earlier stage the optimum temperature for dephosphorization is 1 320 ~ 1 355 ℃ and the suitable basicity of slag is 1.3 ~ 1.6, and the commercial production test of 4 heats of steel DC04 by 210 t top and bottom combined blowing converter has been carried out. Results show that with the controlling measures including 60% ~80% slag amount heels by remaining slag operation, blowing for 3 ~4 min then carrying out the skimming earlier slag operation, and adding green dolomite 10 kg/t and pellet 15 kg/t  ingredient of earlier slag sample being 33% ~39% CaO and 20% 〜25% SiO₂ (basicity L 3 〜1. 6) , in later stage secondary slagging adding lime 16 /t, pellet 15 kg/t and light-burned dolomite 10 kg/t, ingredient of later slag sample being 44% ~47% CaO and ≤15% SiO₂ (basicity 2. 85 - 3. 20) , during tapping by double slag method the average [P] is 0. 014% , the yield of [ Mn ] is ≤30% , and the TFe content in slag in earlier stage is 8. 0% ~ 12% , that has not appreciable influence on the TFe content in slag in later stage.