The endurance time method (ETM) is a novel dynamic analysis method in which artificially intensified accelerograms characterized by the increase in seismic intensity with respect to time are used as loading inputs. In this method, various dynamic responses from elastic to failure range under seismic excitations of different intensity levels are estimated with a reduced dynamic calculation effort. Based on these merits, this paper investigated the accuracy and effectiveness of ETM in predicting the seismic responses and damage of continuous rigid-frame bridges considering real internal force state (named element initial strain state) of the completed bridge. A typical irregular continuous rigid-frame bridge was selected as the analyzed target, a finite element model considering real construction process was established by MIDAS/Civil, and real internal force state considering the 10-year concrete shrinkage and creep was determined through construction phase analysis. Then a dynamic analysis model considering real internal force state was built via OpenSees by means of the equivalent load method, and the incremental dynamic analysis (IDA) results with natural ground motions were obtained to make a comparison. By the ETM, seismic responses of pier displacement, girder displacement and pounding force are analyzed, and the damage of piers is analyzed and evaluated by displacement ductility factor and Park-Ang damage index. The results indicate that ETM can predict the time when continuous rigid-frame bridge reaches a certain damage status under the real internal force state of the completed bridge. In addition, the damage of the main bridge pier is smaller than that of the approach bridge pier when the endurance time is short, but when the endurance time is long, the opposite is true.