Abstract: Mold flux films were made molten slag was cooled to room temperature in graphite crucible at 2°C/min in MoSi2 high temperature resisting furnace, and the crystalline phase were analysed by petrographic microscope. The results showed that: (1) the crystalline phases are mainly the cuspidine, wollastonite and gehlenite with nepheline, fluorite and olivine in some samples under the experimental conditions; (2) with the bacisity and CaF2 content increasemeng, crystalline proportion of mold flux rises with the cuspidine growing, thus the fluorite comes into being with more CaF2; (3) Na2O accelerates the nepheline to come into being; (4) the crystalline portion of mold flux increases with the increasing mass fractions of Li2O, Na2O and K2O with the cuspidine growing; (5) with more MgO found, the form of cuspidine is restrained with wollastonite growing; (6) with more Al2O3 found, the form of cuspidine is restrained with nepheline growing, (7) the crystalline proportion lowers with the increasing mass fractions of BaO and MnO.