Abstract: The effects of phosphorus content in molten steel, tapping temperature, tapping carbon content and slag composition on the dephosphorization of ladle were studied by thermodynamic calculation. According to the results of thermodynamic analysis, the production test of dephosphorization in ladle was carried out. The results show that the dephosphorization reaction can be promoted by reducing the end-point carbon content of converter, increasing the basicity of slag and controlling the mass fraction of FeO in slag at about 17%. The mass fraction of final carbon content of converter is about 0.05%, the basicity of ladle slag is 5.3-7.9, the mass fraction of FeO content is 15%-20%, the dephosphorization rate of ladle can reach 50.0%-72.2%, with an average of 62.9%. When using ladle dephosphorization process to produce low phosphorus steel, the mass fraction of phosphorus in converter tapping can be controlled within 0.025%, the mass fraction of finished product can be controlled within 0.010%, and the smelting period of converter can be reduced from 33.7 min to 30.5 min.