Abstract: By testing with a 80kg vacuum induction furnace and measuring continuous cooling transformation (CCT) curves by using Gleeble 3800 hot simulation machine the chemical composition of steel S2 (/%: 0.63~0.69C, 1.00~1.20Si, 0.40~0.60Mn, 0.20~0.40Cr, 0.40~0.50Mo, 0.15~0.25V, 0.10~0.30Ni, 0.010~0.030Nb, ≤0.015P, ≤0.010S) has been designed, and the commercial production by 120t BOF-LF-VD-300mmx390mm bloom casting-breakdown-high speed wire rolling-Stelmor control cooling process has been carried out. With the process measures including hot metal dephosphorization, sulphur content in metal ≤0.010% , control of BOF end[C] 0.10% ~0.30% , end[P] ≤0.012% , liquid end temperature 1620~1660℃, using Si-Mn pre-deoxidation in BOF tapping, LF refining slag (/%: 8~10MgO, 44~45CaO, 5~10SiO₂,25~35Al₂O₃,feeding calcium wire at end of LF refining, overheating extent of casting liquid ≤25℃，casting speed 0.65m/min, and controlling cooling after rolling, the cqil of alloy tool steel S2 is successfully developed. Examination results show that the each property index of Φ8mm hot-rolled coil meets the requirement of technical specification, including the austenite grain size rating 8.5~9.0, the depth of decarburization layer≤0.5%D, the HRC hardness value of hot-rolled coil 50 and the variation of HRC hardness value of same coil less than 6.