The beam-to-beam impact behavior during the progressive collapse progress of reinforced concrete frame structures under severe ground motions is studied in which three types of impact are included, i.e. 1) contact-impact between one-end failed active beam and intact passive beam; 2) contact-impact between two-end failed active beam and intact passive beam, and 3) contact-impact of one-end failed active beam and one-end failed passive beam. As the first step, the initial impact conditions are established based on the principles of the kinematics and the structural dynamics. Then, the velocities of the beams at the impact instant and the locations of the impact would occur are derived. A so-called impact mass factor is introduced in the paper and determined through the principle of equivalent energy. The history of contact force between the beams involved in the impact is evaluated by the Hertz-damp model. The responses of the passive beam are calculated by solving the equation of motion of a generalized single degree of freedom system.