Abstract: An experimental investigation was done for the physical characteristics of the binding phase in fluorine-containing sinter used in Baotou Steel, especially its fluidity. By readjusting the basicity of the binding phase, i.e. w(CaO)/w(SiO2), and the content of MgO, CaF2 and FeO and measuring the viscosity and surface tension of the as-molten binding phase, the physical changing behavior of the binding phase was found. The results showed that if the basicity is 1.4 the viscosity and melting temperature of binding phase are both the lowest while the surface tension increases with rising basicity. Adding properly the MgO into the sinter can lower the viscosity of binding phase, while the surface tension increases with increasing content of MgO and the melting temperature becomes the lowest if MgO is 5wt%. Adding CaF2 can obviously decrease the viscosity and surface tension. The viscosity and surface tension decrease with the increasing content of FeO.