The dissolution behavior of lime in two groups of slag systems under static conditions was studied by introducing lime blocks with an average size of φ15 mm?10 mm into CaO?SiO2?FeO and CaO?SiO2?FeO?P2O5 slag at 1400℃. The results showed that four areas were formed along reaction interface around in two slag, namely base slag layer, C2S permeable layer, calcium ferrite permeable layer and lime layer. C2S permeable layer and calcium ferrite permeable layer were formed by the interpenetration of Ca2+ in lime and Fe2+ in liquid slag. The presence of a dense solid phase layer in the permeable layer affected the dissolution of lime. The calcium ferrite layer in the permeable layer was gradually replaced by C2S layer. The thickness of C2S layer increased and reached maximum. Finally C2S layer was dissolved in liquid slag. The dissolution rate of lime in the two groups of slag was similar in reaction time of 5~60 s, and the dissolution rate of lime in phosphorus-containing slag was significantly accelerated in reaction time of 60~80 s. When P2O5 was added to the slag, phosphorus was dissolved in C2S to form a C2S?C3P solid solution layer. The formation of this layer will displace FeO into the slag, improve the permeability of the slag, and accelerate the dissolution of lime.