The main span cross of the bridge in this paper appeared the serious down-warping plant disease causing by long-time operation and temperature stress.The bridge was reformed by using external prestressed strengthening technology.During the reinforcement,we confirmed the design of externally prestressed and proposed the calculation formula of the deflection after reinforcement process.The error between monito-ring results of deflection monitoring stations and calculation results of deflection formula was less than 5%.The results showed that the deflection calculation formula after externally prestressed reinforcement was correct and the externally prestressed reinforcement technique is the effective method to reduce the deflection.