There are many hidden joint planes in columnar jointed rock mass. The failure mode of columnar jointed rock mass is different from that of ordinary rock mass due to the crack of hidden joint plane. Its failure mode is mainly influenced by the extremely developed joint and high geostress. Because of the extremely developed joint in columnar jointed rock mass, the failure mode controlled by rock mass structure is the main part of damage mode, which includes joints plane slip (collapse) under single free face, joint plane slip (collapse) under multiple free faces, joint collapse combined with dislocation interface and fault, etc. The failure mode controlled by geostress is the second part of damage mode, which includes concrete layer cracking at crown of valley side. The failure mode controlled by the combination of geostress and rock mass structure is the third part of damage mode, which includes jointed rock mass caving at the lithologic boundary, etc. The failure mode at the surface of columnar jointed rock mass is tension cracking of the joint between columns and joint inside the column. Shear cracking of the joint between columns mainly happens in the surrounding rock. So the corresponding support of columnar jointed rock mass should mainly include two aspects: the shotcrete with steel fiber is mainly to prevent the tensile cracking at the surface of columnar jointed rock mass, and the anchor system is mainly to control the shear failure inside the columnar jointed rock mass.