The invention discloses an arch bridge buckling characteristic coefficient increase based half-through steel arch bridge reinforcement method. An inverted arch is arranged below a main arch ring arch rib of a half-through steel arch bridge, the inverted arch and the arch rib are connected through oblique rods, and the inverted arch and an original arch rib are connected by inverted arch connectors welded to the original arch rib, so that the inverted arch structure for reinforcement and an original main arch ring form a rigid restraint supporting system; the arch bridge buckling characteristic coefficient increase degree in the rigid restraint supporting system is in close relation with seven parameters of the inverted arch and a to-be-reinforced arch, and by setup of different variable values of the seven parameters, a mid-span moment ratio of the to-be-reinforced arch and the reinforced arch is used as a bending moment change characterization quantity to obtain a relation between the seven parameters and the bending moment change characterization quantity on the basis of a finite element parameter analysis fitting method. In application of the arch bridge buckling characteristic coefficient increase based half-through steel arch bridge reinforcement method, a structural characteristic internal force can be solved according to the relation, and accordingly an optimal scheme can be selected for inverted arch reinforcement.