Due to the ［Al］ reaction with the CaO-SiO2-based mold flux used in the high-Al steels continuous casting processes, decreasing the SiO2 content is decreased and the Al2O3 content in mold flux is increased, thus converting the original CaO-SiO2-based mold flux into a CaO-SiO2-Al2O3-based mold flux. This conversion of the mold fluxes can cause the problem of high-Al steels continuous casting. Hence, study on the structural characteristics of the CaO-SiO2-Al2O3- based mold flux can provide fundamental data to design optimum fluxes for high Al-containing steels. In this paper, the structural characteristics of the CaO-SiO2-based and CaO-SiO2-Al2O3-based flux were studied by Raman spectroscopy. The results have shown that, the CaO-SiO2-based flux was the silicate structure whose main micro-structure units were Q0, Q1, Q2 and Q3. The network breakers prefer to depolymerize the silicate network in CaO-SiO2-Al2O3-based flux. While the CaO-SiO2-Al2O3-based flux with low SiO2 content, the ［AlO4］ tetrahedron was entered the silicate network and the melt converted into the aluminosilicates structure, the formation of Al-O-Al linkages and Si-O-Al linkages increased the degree of disorder of network. The results of Li2O replace Na2O and CaO replace MgO have shown that the ions will influence the formation of ［AlO4］ tetrahedron linkages. CaF2 replace CaO shown that the polymerization degree of mold slag decreased first, and then increased with the content of CaF2 more than 13 mol%. So, the influences of the ions type and the ions content on the structure were both need considered while designing the CaO-SiO2-Al2O3-based flux.