The high-temperature rheology of bituminous coal slag in the reducing atmosphere was investigated in this study. The characteristics of slag sample were analyzed by multi-techniques. The rheological measurement of the slag was carried out by a high-temperature rheometer at temperatures of 1360-1460?. The effects of the shear rate and temperature on the rheological property of the slag were studied. The volume fractions of crystallize particles and mineral matters variation were predicted by thermodynamic software FactSage. The results show that the viscosity and shear stress of the slag increase with decreasing temperature at the constant shear rate. When the volume fraction of the crystallize particles is less than 10%, the slag behaves as a Newtonian fluid. When the volume fraction of the crystallize particles is more than 15%, the slag viscosity decreases with increasing shear rate. The non-Newtonian fluid behavior of slag is illustrated by shear thinning behavior and thixotropic behavior. With decreasing temperature, the shear thinning behavior becomes increasingly significant. In addition, the viscosity prediction model basing on S2 model and Einstein-Roscoe model was established.