During the operation of existing steel truss bridges, structural rigidity decreases compared to its initial state due to damage to geological conditions and fatigue aging and corrosion of bridges. With an existing steel truss bridge as the research object, the finite element model was verified with the strain and deformation data collected on site, and the stress characteristics of the bridge structure during the jacking construction stage were analyzed depending on the changes in stiffness and temperature parameters. Numerical analysis results show that the deformation of the bridge structure is greatly influenced by the loss of stiffness and temperature changes during the reinforcement and jacking of the bridge. When the stiffness of the entire bridge is reduced by 10%, 15%, and 20%, the maximum deformation of the bridge increases by 12.5%, 20.0%, and 25.3%, respectively. When the temperature difference is 20 ℃, the maximum vertical and longitudinal deformation of the bridge is 15.7 mm and 35.1 mm, respectively. This research can provide reference for the reinforcement and jacking of the same type of steel truss bridges.