To address the issue of high auxiliary material consumption in the less-slag process, the thermodynamic conditions of the dephosphorization reaction in the “slag retention and double slag” smelting process and the influence of initial and endpoint slag compositions on converter dephosphorization ratio were investigated. The results indicated that the initial slag exhibited strong dephosphorization capability and its optimal composition was a basicity of 1.2-1.5 and w (MgO) less than 6%. The amount of initial auxiliary materials was calculated based on material balance to achieve the target slag composition. The results also indicated that the basicity of endpoint slag could be reduced from 3.27 to 3.08 when the endpoint temperature was lowered from 1 660 ℃ to 1 645 ℃, achieving equivalent dephosphorization efficiency with lower auxiliary material consumption. After optimizing the converter slagging process, auxiliary material consumption was significantly decreased without increasing endpoint phosphorus content. Specifically, the lime consumption was decreased from 26.01 kg/t to 23.36 kg/t, and the consumption of calcined dolomite was reduced from 13.91 kg/t to 9.2 kg/t.