Shear lag effect of continuous curved box girder with three spans under seismic excitation is studied in this paper. Firstly, spatial shell finite element model is founded by ANSYS, and EL-centro seismic wave is chosen as seismic excitation. Secondly, the shear lag effect at different cross sections are investigated with dynamic time-history analysis, the results show that under seismic excitation there is prominent shear lag effect in continuous curved box girder, the maximum shear lag coefficient is 3.02, shear lag effect is severe, shear lag effect at mid-span cross sections are prominent than support cross sections, and inside peak shear lag coefficients are generally greater than outside. Finally, the numeric results are compared with the experimental results from a vibration table testing, which shows great consistencies.