Abstract: Taking the base slag system of low-reactive CaO-Al₂O₃-Li₂O-B₂O₃-CaF₂ mold fluxes as the object, and with the aid of equipment such as the single hot thermocouple technique, scanning electron microscope, and X-ray diffraction analyzer, the effects of substituting B₂O₃ for CaF₂ on the properties of the slag such as crystallization temperature, critical cooling rate, crystallization incubation time and crystalline phases were investigated, and the crystallization kinetics analysis was carried out. The results show that using B₂O₃ instead of CaF₂ can effectively reduce the crystallization tendency of the slag. When the w（B₂O₃）/w（CaF₂） ratio increases from 0.44 to 2.25, the critical cooling rate rises. When the ratio of w（B₂O₃） to w（CaF₂） is 2.25, the critical cooling rate reaches 12 ℃/s, and the crystallization performance is the weakest. With the increase of the substitution amount of B₂O₃ for CaF₂, the crystallization inoculation time shows a trend of first increasing and then shortening. During the cooling process of the slag, the initial crystalline phase formed changes from CaAl₂O₄ to CaAl₄O₇. The change law of the full crystalline phase is CaAl₂O₄+CaF₂→CaAl₄O₇+CaF₂→CaAl₄O₇+CaF₂+Ca₅B₃O₉F. Kinetic analysis indicates that when w（B₂O₃）/w（CaF₂） is less than 1.6, the crystal growth changes from three-dimensional to two-dimensional as the temperature drops, with a transition temperature of 1 100 ℃. When w（B₂O₃）/w（CaF₂） is greater than or equal to 1.6, the crystals precipitated in the slag always grow in three dimensions. Moreover, as the substitution amount of B₂O₃ for CaF₂ increases, the precipitation of Ca₅B₃O₉F promotes the three-dimensional growth of the crystal. When the ratio of w（B₂O₃） to w（CaF₂） is 0.625 to 1, the crystallization performance of the slag is relatively weak, and the types of crystalline phases are fewer, which is more conducive to the regulation of crystallization performance.