In order to overcome the defect that the impact velocity is assumed between blades and foreign object in present method, and to deeply search the law for an aeroengine blade impacted by the foreign object from the runway, the impact velocity of foreign object against the aeroengine blade is estimated in the paper. Firstly, taking the tested results as a basis，velocity induced by the air vortex from the runway surface to the inlet port is studied. Then, velocity equation from the inlet port to the blade is deduced by using the momentum theorem. Taking a blade as a reference，expressions of both the impact velocity and the impact direction relative to the blade are found. At last, a certain type of the airplane and its aeroengine are taken as example, the change rule of the motion velocity in inlet channel is studied. The results show that the foreign object motion velocity relates not only with the foreign object shape, dimension and material，but also with the aeroengine working state, the height and the length of the inlet port. The impact direction is out of vertical to the blade surface.