An approach for predicting normal aerodynamic force coefficient of missiles with inlets was developed and evaluated aimed at the problem that the existing aerodynamic estimation method for missiles with inlets can not meet the requirement of aerodynamic estimation in conceptual design. By taking inlet as a wing with tiny aspect ratio, and introducing correction coefficient of the interference factor between body and inlet and correction coefficient of the interference factor between body-inlet assembly and wing, the normal force coefficients of missiles with inlet were calculated using component buildup approach. Results from engineering prediction accord well with result from Computational Fluid Dynamics (CFD), and the maximum error is less than 5%. This method is simple and practical, and can be used in conceptual design and preliminary design of missiles.