Abstract: The flowsheet of steel 27 CrMoNbV at Pansteel is hot metal pretreatment-120 t top bottom combined blown BOF-LF-RH-360 mm x450 mm bloom CC process. With the process optimization including hot metal deep desulfurization pretreatment, BOF double slag dephosphorization process, deep desulfurization in the process of BOF tapping and LF refining with (1. 6 ~2. 2) CaO/Al₂O₃ refining slag system, RH refining treatment by feeding Ca-Si wire and protective casting, the chemical composition stability of steel 27CrMoNbV is produced with P ≤ 0.010% , S≤0.004% , [ H] ≤ 1. 5 x 10^-6 ,T[O] ≤0.0011%. The rating of non-metallic inclusion of A, B, C, D and Ds are all≤ 1.0 rating, which fully meet technical requirements.