Based on the airworthiness specification, the geometry, mass and initial attitude characteristics of two foreign objects: the hail and ice cube, are analyzed and determined. The aerodynamics and trajectories of the foreign objects in engine inlet and bypass duct of turboprop aircraft have been simulated by coupling the Computational Fluid Dynamics (CFD) and six degrees of freedom methods. In view of the possible collision phenomenon in the movements, we further develop a reasonable and effective method combined with LS-DYNA software. The method is verified through a turboprop. The results indicate that once the foreign objects collide with the inlet or bypass duct, they lose their kinetic energy and can be broken into very small pieces, then these foreign objects do less harm to the engine and can be considered to exclude from the bypass duct. However, the ice cubes on the lower wall of the inlet may directly move into the main engine, and cause serious consequences, which should be carefully noted and researched.