The invention discloses an active strengthening method of a multi-span ordinary reinforced concrete beam bridge, wherein a steel arch sheet is added under the multi-span ordinary reinforced concrete beam to be strengthened, a steel support column is arranged between the steel arch sheet and the ordinary concrete beam, and steel tie rods are arranged between the arch feet on both sides of the steelarch sheet. A method for increase arch sheet. A rigid restrained bracing system is formed between the reinforced arch and the original reinforced concrete beam, and a rigid restrained bracing systemis formed between the reinforced arch and the original reinforced concrete beam. The internal force of the beam is reduce, the bearing capacity of the bridge can be greatly improved, the overall rigidity of the bridge to be strengthened can be increased, the crack width of the beam body can be effectively contracted, the durability of the bridge can be improved, and the steel tie rods arranged atthe steel arch legs are favorable for balancing the horizontal force generated by the steel arch legs. The reinforcement construction method of the invention is simple and convenient, the reinforcement process is orderly, the construction quality is easy to control, the operability is strong, and the effect is obvious. Under the action of upward vertical force, the concrete beam can reduce the bending moment in the middle span, shrink the crack width at the bottom of the beam, and increase the bearing capacity of the strengthened concrete beam by more than 30%.