The bridge's dynamic features and train's running comfort under resonant speed of simply supported beams with equal spans are analyzed. Through calculation, we know that the simply supported beams with equal spans and the trains will have one to two resonant speeds during high speed, the bridge's dynamic factors between different spans have little change, and the train's running comfort differs a little during no.1 to no.4 while, from no.5 span, it becomes stable. This means that the railway simply supported beams with equal spans arc suitable used for extra-long bridges.