A study for the nonlinear analysis method of curved concrete girders strengthened with externally prestressed tendons is presented. The curved concrete girders with external tendons exhibit complex nonlinear behavior due to the slip of external tendons at deviator and the change of eccentricity between the member and external tendon in addition to the distortion of the girder due to the prestressing forces. The external tendon between anchorage-deviator or deviator-deviator is modeled as an assemblage of the curved elements. The slip effect of the external tendon at deviator is taken into account using the force equilibrium relationship between the friction force and the driving force at each deviator. The finite element model and analysis method of the external tendon are integrated into the nonlinear analysis program of three-dimensional PSC frames developed by the authors. The capability of the proposed analysis method is demonstrated through the nonlinear analysis of curved concrete girder bridge strengthened with exterally prestressed tendons during the service life of the bridge. It is found that the proposed analysis method is capable to predict the nonlinear behavior of curved concrete girder bridge strengthened with exterally prestressed tendons at any time during the service life of the bridge and strengthening the curved girder with external tendon is advantageous in reducing the vertical, horizontal deflections and stresses, but disadvantageous in reducing distortional moment of the girder.