Abstract: Dephosphorization treatment was utilized in the clean steel process in Shougang Jingtang Iron & Steel United Co. Ltd. Based on the first 58 heats tests,the practical operation process were established,especially for slag making,oxygen injecting,and temperature controlling. The stable and efficient method for low-P content and ultra-low-P content steel production was obtained. According to the experiments results,the average P content (mass fraction,so as the following) in the dephosphorization converter is 0.017%,the C content is 3.69%,and the converter terminal temperature is 1 350℃. Moreover,the P content of 10 heats is below 0.015% with the lowest content of 0.008%,which meets the requirement of ultra-low-P steel. The factors which can affect the dephosphorization process,such as silicon content,carbon content,converter terminal temperature,slag basicity,and oxidizability were investigated. The results demonstrate that when the silicon content is below 0.45%,dephosphorization is relatively more efficient. As the converter terminal temperature increases,the dephosphorization result becomes worse; however,to guarantee the temperature in the de-carbon converter,the dephosphorization converter terminal temperature is fixed at 1 350 to 1 380℃. The reasonable carbon content in the dephosphorization converter is 3.3% to 3.8%. To meet the dephosphorization requirement,the basicity (R) is controlled between 1.8 and 2.2. Enhancing the ore addition and keeping the higher lance position are suggested to increase the FeO content in slag to increase the dephosphorization efficiency.