Mixed-phase icing of supercooled droplets and ice crystals is one of the new challenges in the field of aircraft icing. The Euler method is applied to solve the impact characteristics of ice crystals and supercooled droplets. The heat and mass transfer processes after the impact of ice crystals and supercooled droplets on the surface are analyzed, and an icing thermodynamic model is established. The effects of ice crystal adhesion, melting, and erosion on surface quality are studied, and a solution method for the governing equations is given. Numerical simulations of mixed-phase icing under different operating conditions are conducted. Comparison with experimental results demonstrates the accuracy of the method used in this paper. Numerical simulations of mixed-phase icing with different parameters show that the amount and extent of icing on the airfoil surface increase with increasing droplet content. Increasing ice crystal content and diameter also increases the amount of surface icing, but the increase is relatively small. As the incoming flow velocity increases, the amount of icing gradually increases. As the angle of attack increases, the icing area gradually shifts towards the lower surface. When the icing temperature of the mixed phase is low, the icing type is rime ice, and the change in icing shape is smaller. In this case, the airfoil's maximum lift coefficient decreases by 31.0%. When the icing temperature is high, the icing type is glaze ice, and the amount and extent of icing increase compared to supercooled droplet icing. In this case, the airfoil's maximum lift coefficient decreases by 60.8%. The detrimental effect of icing on the airfoil's aerodynamic characteristics is significantly greater under glaze ice conditions than under rime ice conditions. The research content of this paper can provide technical references for related icing research and anti/de-icing design.