Abstract: The viscosity,softening temperatue and melting temperature of blast furnace slag with different basicity had been investigated in this paper.The results show that Baogang's BF slag is typical of short slag,when the temperature is above 1 400℃,the slag has very low viscosity is very low(about 0.5 Pa·s) and good fluidity.The viscosity and the melting temperature increase with increasing the slag basicity up to 1.07.Further increasing basicity leads to the reduction in both viscosity and melting temperature.The equilibrium reaction and its phase diagram obtained by the Factsage thermodynamic software indicates that the slag basicity of 1.13 is in favor of reducing coke ratio.