The invention relates to a reinforcement method for pre-stress continuous beam base plate cracks. A continuous beam midspan base plate is cracked after a pre-stress pipeline is grouted, so that the maintenance and the reinforcement can not be finished by using a method for re-tensioning pre-stress steel bundles in a beam body. The reinforcement method comprises the following steps of: digging off concrete formed by cracking of the base plate; symmetrically and uniformly applying a pre-stress load to layered stacks from the two sides to the middle within a midspan range; embedding new reinforcement steel bars into drilling holes, resetting steel bar meshes on the top layer and the bottom layer of the conventional base plate, binding and fixing the steel bar meshes, and cleaning floating slurry on the surfaces of the steel bars; and after the concrete achieves the strength, symmetrically and uniformly unloading from two sides to the middle until the load is zero, wherein an elastic upper arch of a beam body pressurizes the base plate, so that a top plate is decompressed; and therefore, pre-stress is applied, and a reinforcement effect is achieved. By using the mechanical characteristics of the stress on a continuous beam, the pre-stress load is applied to a cracked section, and natural pre-stress is supplied to the cracked section; and therefore, the reinforcement construction difficulty and the construction cost are reduced, and consequences caused by the high stress and high creepage are avoided.