Abstract: In order to develop fluorine-free mold fluxes into stable properties for slab continuous casting of low carbon steel, the formation regions of fluorine-free mold fluxes were investigated. Based on the test of the physical properties of traditional fluorine containing (F^- ≥ 3%) fluxes, the slag samples, fitting to the compositional characteristics of mold fluxes, were designed by using the mathematical complex method in the slag system of CaO-SiO₂-Al₂O₃-Fe₂O₃-MgO-Li₂O-TiO₂-Na₂O-MnO-B₂O₃. By fixing some variable components step by step, the multidimensional composition space was transformed into two-dimensional plain grids, from which the nodal points were used as compositions of fluxes. Compared with the properties of fluorine containing fluxes, three formation regions of fluorine-free fluxes, with a lower basicity, melting point, viscosity and breaking temperature, and solidified in the glassy state, were found. The typical components in one of the regions were CaO 31.2%, SiO₂ 36.8%, Al₂O₃ 3%, Fe₂O₃ 1%, MgO 2%, Li₂O 2%, TiO₂ 6%, Na₂O 7%-12%, MNO 3%-8%, and B₂O₃ 0-3%.