Abstract: This paper studies the low phosphorus steel smelting process in the top and bottom combined blown converter.After dephosphorization pretreatment of hot metal and then deslagging in semisteel procedure,the same converter was used to smelt ultralow phosphorus steel with the remaining part of slag.The results show that with phosphorus content of 0.13% in the hot metal,basicities of semisteel and the final slag is controlled at around 2.0 and 3.6 respectively,total iron at 18% or so,deslagging volume of semisteel at 40% to 60%,the dephosphorization rate of semisteel peaks at 65% with an average of 50%,and dephosphorization rate of the final steel peaks at 98% with an average of 94.6%;phosphorus content in the final steel can be controlled under 0.007% with the minimum of 0.003%,satisfying the requirements of low phosphorus steel.