To investigate the seismic isolation effect of double spherical seismic isolation (DSSI) bearings in the simply-supported railway bridges, the finite element models (FEM) of those bridges with pier height of 8m and 25m were established by the ABAQUS software, and were studied by a nonlinear dynamic time-history analysis under earthquakes. Based on the comparison of finite element calculation results and shaking table test results, the correctness of FEM was verified. The dynamic behaviors, including horizontal sliding displacement, vertical displacement and vertical load change of DSSI bearings under earthquakes, were analyzed and compared with the traditional spherical steel bearings. The horizontal sliding displacement range of DSSI bearings under different seismic intensities was obtained. The results show that when compared with the traditional spherical steel bearings, the DSSI bearings can significantly reduce the vertical relative displacement between the fixed end and the sliding end of the simply-supported girder under longitudinal earthquake effects in most cases, and have less detrimental effects on track structure. The DSSI bearings can significantly reduce the amplitude of vertical load of bearing under transverse earthquake effects and can effectively avoid the separation and collision of sliding surface of bearing.