Abstract: Unloading damage characteristics of columnar jointed basalt was obvious at Baihetan hydropower station. In the aim of obtaining the unloading damage law of this special rock mass, deformation and strength tests were both conducted to obtain the quantitative expressions of columnar joint’s stiffness and strength during unloading test, and then a numerical calculation method in consideration of unloading damage was proposed in association with element method. On this basis, a discrete element numerical model of columnar jointed basalt was established for the research of damage law of columnar jointed basalt during excavation-induced unloading. Results revealed that in the process of unloading parameter decreasing from 6.0 MPa to 1.0 MPa, vertical and horizontal elastic moduli reduced by 64.8% and 86.3%, respectively, cohesive forces in the two directions reduced by 18.3% and 46.1%, respectively, and angles of internal friction decreased by 8.4% and 64.7%, respectively. In other words, the unloading damage characteristics of columnar jointed basalt was significant, and the deformation and strength parameters both reduced remarkably during unloading and the reduction was more serious in horizontal direction than that in vertical direction. The study results could be taken as reference for selecting excavation types and supporting forms in similar projects.