Abstract: The material balance of sulfur and the influencing factors of desulphurization of smelting 45^# hard wire steel in 70t top and bottom combined blowing converter were analyzed. Based on that, according to the conditions of the raw materials, content of sulfur in furnace was controlled, and the operation parameters of desulphurization in converter were optimized to achieve the effective control of end sulfur. The application results show that the total content of sulfur in the furnace is less than 10kg, the basicity of converter slag is 3.5-4.0, mass fraction of FeO in the slag is 10%-20%, and the end point temperature of converter is at 1630-1650 ℃, the resulphurization in the end of the converter is reduced, and at the end point the average sulfur content of resulphurization decreases from 0.007% to 0.004%, the qualification rate of end sulfur increases from 70% to over 96%.