Abstract: The dynamic parameters of unstable rock mass can characterize the damage of structural plane between dangerous rock mass and bedrock. How to identify the dynamic parameters of dangerous rock mass according to the micromotion characteristics of the site is still an urgent problem to be solved. Based on this problem, a dynamic feature recognition method of dangerous rock mass based on constant micromotion excitation is proposed. 1) The first-order natural frequency of dangerous rock mass is most easily excited and identified. The vibration problem of dangerous rock mass under constant micromotion excitation can be classified as the forced vibration problem of single degree of freedom structure under underdamped condition. 2) Under the constant micromotion excitation, the ratio of the spectrum amplitude of the dangerous rock mass to the spectrum amplitude of the bedrock is used as the relative amplitude spectrum, and the first-order natural frequency is identified by the relative amplitude spectrum. 3) The bedrock is the excitation source relative to the dangerous rock mass. When the mechanical wave propagating from bedrock to dangerous rock mass passes through the porous damage structure plane medium, the mechanical wave is scattered. The frequency domain of mechanical wave changes. The variation of dynamic parameters of cantilever dangerous rock mass, shear fractured dangerous rock mass and sliding dangerous rock mass model with structural plane damage is analyzed by indoor model test. The following conclusions are drawn: 1) Based on the theory of vibration mechanics, the first-order natural frequency of dangerous rock mass can be obtained according to the relative amplitude spectrum. 2) The structural plane damage of unstable rock mass controlled by macroscopic cracks can be identified by the first natural frequency of dangerous rock mass. There is no obvious change in displacement during the damage process of the structural plane of the micro-crack-controlled dangerous rock mass. The first-order natural frequency of dangerous rock mass also remains basically unchanged. The change trend of center frequency can reflect the development of cracks and then identify the damage degree of dangerous rock mass. 3) For dangerous rock mass with single structural plane, it is limited to analyze the damage of structural plane of dangerous rock mass only by using vibration mechanics theory or elastic wave scattering theory. It will be more effective to identify the structural plane damage of unstable rock mass by combining the theory of vibration mechanics or elastic wave scattering theory.