Abstract: Based on the chemical compositions of steel slags from domestic iron and steel enterprises, CaO(50%)-MgO(10%)-SiO₂(10%)-Fe₂O₃(30%)(mass fraction)slag was chosen as basic experimental synthetic slag system.After experiment of calcination and melt, the plase, topography and microstructure were analyzed with X-ray diffraction, scanning electron microscope and spectrometen, the influence of basicity and P₂O₅ content on selfpulverization was studied. The results show that controlling the basicity with R≈2.5, when slag particle size is less than 150 μm, the slag has the best effect of self-pulverization, and slag pulverization rate can reach 94.33%; when the mass fraction of P₂O₅ in slag is less than 0.125%, the slag can achieve self-pulverization.