The invention discloses a columnar jointed rock mass slope anchor cable supporting method. Drilled holes are arranged in rows, and the holes in the corresponding positions in every two adjacent rows are staggered by a certain distance in height. Two drilled holes are formed in the same hole position and are in the leftward direction and the rightward direction respectively. Each left drilled hole and the corresponding right drilled hole are formed in the same plane, and the plane is perpendicular to the columnar jointing axial direction. Therefore, a three-dimensional anchor cable network perpendicular to the columnar jointing axial direction is formed. The defects that in the traditional technology, anchor cable stress is unreasonable, and the supporting effect is poor are overcome. The three-dimensional anchor cable network is formed, anchor cable stress is reasonable, and the supporting effect is good.