While excavating the rock mass by drilling and blasting method,it is bound to cause a certain degree of damage to the surrounding rock.Therefore,it has an important guiding role for the tunnel support design and longterm stability to make clear the damage characteristics of the surrounding rock during tunnel blasting excavation.Taking the blasting excavation of the Longnan Tunnel of the GanzhouShenzhen Highspeed Railway under Class Ⅲ surrounding rock as an example,the crosshole ultrasonic detection method was used to detect the acoustic wave velocity of the surrounding rock in different parts of the same crosssection of the tunnel,and the distribution characteristics of the acoustic wave reduction rate were analyzed.Based on the analysis,the damage depth of the surrounding rock in different parts of the tunnel was determined,and the relationship between the damage degree and the damage depth of the surrounding rock was revealed.Based on LSDYNA numerical simulation software,the damage evolution and distribution characteristics of the surrounding rock under 8 cyclic bench blasting under the same working conditions are simulated,which are basically consistent with the damage distribution characteristics evaluated by the acoustic wave test.The analysis results show that the surrounding rock at the foot of the arch at the upper bench has the greatest degree of damage,but with the shallowest damage depth.The maximum depth of damage to the surrounding rock is located at the bottom of the inversion arch.Based on the damage distribution characteristics,and according to the engineering analogy and relevant standards,the length of the initial supporting bolts of the grade Ⅲ surrounding rock of Longnan Tunnel should be 3.5~4 m.