Taking the prestressed concrete simple T-shape beam bridge with common span of 16，20，24 and 32m as an example，the 3-D finite element model of the coupled heavy haul train-track-bridge system was constructed to study the impact of increasing load of heavy haul train on the structural response of prestressed concrete simple T-shape beam bridges in existing railways． The accuracy of model was verified by a case study of a typical pre-stressed concrete simple T-shape beam bridge in Shuo-Huang railway． The dynamic response of the train-bridge system under heavy haul train was calculated，the influencing rule of increasing load of heavy haul train on the dynamic responses of railway bridge structure was discussed． And the adaptability of increasing load of heavy haul train in typical bridges of the existing railways was also analyzed． The results show that when using the same kinds of freight trains，the displacement responses of the each span bridge increase linearly as the axle load of freight train increase，and the acceleration responses increases with the increase in the axle load of freight train． When using different kinds of freight trains，the dynamic responses of each span bridge fluctuated with the increase of the axle load，and the relationship between its change and the increase of axle load is not obvious． The length of train body and vehicle distance have a big influence on long-span bridges． When the span is small (less than 8m)，the dy-namic response of the heavy haul train to the bridge is only concerned with the wheelbase． When the train axle is lifted to 30t and above，the lateral dynamic response of typical railway bridges is rather large，so lateral reinforce-ment should be carried out．