The isothermal and non-isothermal experiments were performed to construct the continuous cooling trans- formation (CCT) and temperature time transformation(TTT)diagrams of four industrial mold fluxes through visual observations in an experimental apparatus based on the single hot thermocouple technique(SHTT).The results of the CCT diagrams indicate that①the crystallization temperature of mold fluxes lowers as the cooling rate increases,②the mold fluxes have larger critical cooling rate,higher crystallization temperature, and less onset time of crystal- lization when the basicity increases or the viscosity decreases,③the influences of the melting points of the mold flu- xes on their crystallization tendency are not significant.Isothermal tests show that the onset time of crystallization decreases at first, and then increases, and finally represents a“C”shape with increasing isothermal temperature. The TTT diagrams of four industrial mold fluxes were divided into two separate“C”shape regions. The crystal phase of C20A selected was analyzed by X-ray diffraction, which is cuspidine (Ca_4 Si_2O_7 F_2) over 1100℃and calci- um silicon oxide fluoride (Ca_2SiO_2F_2) below 1100℃.When compared with the TTT diagram, the CCT diagram can provide a more realistic estimate of the critical cooling rate of the mold fluxes. Thus, both the CCT and TTT di- agrams can unambiguously describe the crystallization phenomena of the mold fluxes. The isothermal and non-isothermal experiments were performed to construct the continuous cooling trans-formation (CCT) and temperature time transformation (TTT) diagrams of four industrial mold fluxes through visual observations in an experimental apparatus based on the single hot thermocouple technique (SHTT) . The results of the CCT diagrams that that ① the crystallization temperature of mold fluxes lowers as the cooling rate increases, ② the mold fluxes have the larger critical cooling rate, higher crystallization temperature, and less onset time of crystal temperature, and less onset time of crystal-lization The influences of the melting points of the mold flu-xes on their crystallization tendency are not significant. Isothermal tests show that the onset time of crystallization decreases at first, and then increases, and finally represents a “C” shape with increasing The TTT diagrams of four industrial mold fluxes were divided into two separate “C ”crystal regions of C20A selected was analyzed by X-ray diffraction, which is cuspidine (Ca_4 Si_2O_7 F_2) over 1100 ° C. the CCT diagram can provide a more realistic estimate of the critical cooling rate of the mold fluxes. Thus, both the CCT and TTT di- agrams can unambiguously describe the crystallization phenomena of the mold fluxes.