Liquid film formation is an important part of the air quenching dry slag granulation process and the granulation effect of slag depends on the film flow characteristics. To investigate the flow behavior of slag and the effects of different operating parameters and slag properties on the film flow characteristics, a three-dimensional unsteady numerical model was established using k?? based shear stress transport (k?? SST) turbulence model and the coupled level-set, and the volume of fluid (CLSVOF) method was utilized to capture the sharp air?liquid interface. The film formation mechanism and the influence of different operating parameters and slag properties on the film flow characteristics were discussed. Also, dimension analysis of the film edge thickness was conducted. The results indicate that the flat film was formed because of flow deformation due to air impingement, recirculation zone, and pressure gradients. An unstable wave appeared on the film surface owing to the gas?liquid velocity difference. The wavelength of surface wave decreased first and then increased along the axis, and the film thickness gradually decreased along the axis. The wavelength of surface wave and the film thickness decreased with the increasing airflow velocity and increased with the rise in slag mass flow rate. The wavelength of surface wave and film thickness decreased with the increasing slag density and increased with the rise in slag viscosity. A dimensionless was developed which indicates that the film thickness had exponent relation to the airflow velocity, slag mass flow rate, slag density, and viscosity.