The impact on curved box girder bridges due to applying prestressing force have been analyzed using finite element method. This paper presents the results of an experimental investigation and analytical studies. Based on the model experiment, the results and conclusions of shear lag in curved box girder with prestressing force are presented that prestressing force has changed shear lag distribution. The prestressing force action on box girder shall be considered comprehensively, structural force shall be analyzed accurately, optimize prestressing tendons shall be set rationally which would make force more rationally. The results highlighted that the impact factors of a curved box girder bridge have been observed to be generally very high, while those of the other responses are also relatively higher than that of corresponding straight box girder bridge.