Abstract: On the basis of thermodynamic study,with converter steel slag as the leaching object and acetic acid as leaching agent,the effects of leaching temperature,leaching time,concentration of acetic acid and the ratio of solid to liquid on the leaching rate of calcium in converter steel slag having different particle sizes were investigated.The results show that the Gibbs free energy change for leaching reaction of CaO and Ca₂SiO₄ phase is negative while it’s positive for the leaching reaction of the CaTiO₃ phase in the converter steel slag with temperature range of 273.15~373.15 K.The leaching rate of calcium-based active components in the slag are very rapid.The smaller the particle size and the solid-liquid ratio,the higher the leaching rate of the calcium-based active components. Meanwhile,a higher leaching rate of calcium can be obtained at higher concentration of acetic acid.The leaching rate of calcium ion reaches to 87.52% at 1 mol/L of acetic acid,1 ∶ 20 of solid to liquid ratio,70 °C of leaching temperature for 60 min.XRD and SEM analysis shows that the active calcium oxide in the converter steel slag is completely leached with irregular pores formed on the surface of the slag,while calcium titanate （CaTiO₃） stays in the slag.