Abstract: During the blasting excavation process of underground mine tunnels，in order to analyze the instability mechanism of dangerous rock masses，a 1 240 m leveldrift in a certain underground mine in the Western Panzhihua area was selected as the research object. The 3D laser scanning technology was used to identify the characteristics of the dominant structural planes of the rock mass，and on-site blasting vibration monitoring was carried out. Based on the Sadovsky empirical formula and the dynamic reduction coefficient，the equivalent static load borne by the rock mass under blasting was calculated. Finally，using the 3DEC discrete element software，a numerical model was established to systematically analyze the insta⁃ bility evolution process of dangerous rock masses in the tunnel surrounding rock under blasting distur⁃ bance. The results show that the three groups of dominant structural planes developed in the study area form a key geometric configuration through composite intersection，which is the main cause of block insta⁃ bility. It was calculated that the equivalent static load borne by the blocks in the study area under blasting is approximately 1.17g. Through discrete block analysis，two main dangerous blocks were identified，both located in the roof area of the tunnel. Their maximum spans are 1.12 m and 2.03 m，respectively，and their volumes are 0.48 m³ and 1.02 m³，respectively，and they are controlled by two different dominant structural planes and undergo sliding instability. The research results can provide theoretical basis and practical reference for the stability analysis of tunnel，the optimization of support structures，and the safety management of the roof.

Key words: underground mine tunnel, identification of dangerous block , discontinuities characteriza? tion, 3DEC discrete element software