Abstract: The single hot-wire thermocouple technique was used to study the influencing factors on the crystalline temperature of mold flux, and how the different compositions of flux used affect the crystalline temperature was revealed. The results showed that the crystalline temperature of mold flux rises with the increasing basicity, mass fractions of NaF and CaF2 contents, and the crystalline temperature lowers gradually with the increasing mass fractions of Al2O3, MgO, Na2O, K2O, BaO, MnO and B2O3 contents. Furthermore, the crystalline temperature decreases first then comes to its lowest value at 2% with the increasing mass fractions of Li2O content, and goes up from the lowest point later on.