Abstract: The oxidation-reduction reaction can easily happen between Al contained in liquid steel and SiO₂ component in mold fluxes during continuous casting of TRIP steel containing Al.As a result,the Al₂O₃ component sharply increases from 3% to 30%,and the w_(Al2O3)/w_(SiO2) ratio simultaneously ascends from 0.10 to 1.44,so the viscosity could have a bigger fluctuation accordingly.The effects of Al₂O₃ content and w_(Al2O3)/w_(SiO2) ratio on the viscosity of mold slags were investigated for producing TRIP steel containing Al.A model was built to predict the viscosity of the high Al₂O₃ slag system.The results indicate that when the comprehensive basicity is less than 1,the viscosity of mold fluxes initially rises and then reduces again with increasing the Al₂O₃ content from 3% to 17%,but it changes slightly when the basicity is greater than 1.The viscosity of mold fluxes dramatically rises when the Al₂O₃ content changes from 17% to 30%.With increasing w_(Al2O3)/w_(SiO2) ratio,the viscosity of mold fluxes for TRIP steel containing Al initially reduces and then abruptly rises.