Abstract: Perilous rock has a sudden falling feature, which is a dynamic process of rapid energy release. Focusing on the pressure-shear perilous rock, the mechanical model is proposed; and the constitutive equations of locked patch tangential resistance force and shear displacement is established. It obtains that the energy accumulation will release and transform to the elastic and impulsive kinetic energy at the moment of dynamic instability on perilous rock. Meanwhile, it calculates the formulas of fracture extend dissipation energy on the locked patch of dominant fissure. And the evolution curve, which the accumulating and energy release of perilous rock will incrassate with the accretion of shear displacement, is gained. Then, it proposes a method to calculate the elastic and impulsive velocity and acceleration on collapse mass after a sudden collapse. Furthermore, the results provide some scientific basis for further study on collapse mechanism and disaster effects.