The invention relates to a monitoring method for bending deformation of rod members of the existing space steel structure. The monitoring method is characterized by comprising steps that on-site monitoring of the existing space steel structure is performed to generate a three-dimensional point cloud model of the existing space steel structure; fitting and numbering of all the rod members in the three-dimensional point cloud model of the existing space steel structure are performed, and a mark number of each rod member is determined; according to ball nodes of all the rod members in the three-dimensional point cloud model of the existing space steel structure, axis fitting is performed on all the rod members to obtain axis equations of all the rod members; according to the axis equations ofall the rod members, whether the rod members in the three-dimensional point cloud model of the existing space steel structure are subjected to bending deformation is determined; the mark number, theposition and the deformation amount of all the rod members generating bending deformation in the three-dimensional point cloud model of the existing space steel structure are determined. The monitoring method can be widely applied to the field of existing space steel structure monitoring.