Abstract: In order to improve the quality of slag fiber,iron tailings were used for adjusting the blast furnace slag. The effect of acidity on the viscosity,melting temperature and mineral compositions of the adjusted blast furnace slag was investigated,and the quality of slag fiber was evidenced to be improved by changing the acidity coefficient on the basis of centrifuge tests. The results show that with the increase of the addition of iron tailings,the acidity coefficient M_k of the adjusted blast furnace slag increases while its melting temperature decreases first and then increases,and the viscosity value corresponding to the melting temperature increases gradually. Simultaneously,there is no mineral precipitated in the adjusted blast furnace slag,with all the amorphous phase produced after solidification of the molten slag. It is shown that with addition of iron tailings,the properties of blast furnace slag change from short to long characteristic,and slag viscosity changes slowly under the condition of fiber formation. Consequently,the temperature range for fiber formation can be expanded by adjusting the blast furnace slag,and it's beneficial to control the fiber formation. The diameter of the slag fiber with a better using performance can be increased with increase of acidity coefficient M_k.