Abstract: A dynamic model was developed to investigate the elastic impact of helicopter rotor blades.General kinematical relations for a beam theory were established to treat the finite rotation.Hertz' theory of elasticity was presented to treat local elastic deformation.The compatibility equation of displacement was adopted to calculate the impact loads.Dynamic equations of elastic impact of rotor blades were derived by Hamilton principle.In comparison with Timoshenko's example,the validity of the results has been demonstrated.The impact response of helicopter blades under the impact of a lumped mass was also discussed.