Abstract: In studying the reinforcement of steel girder bridges in the project of raising train speeds of China抯 railway, a spatial dynamic analysis model for train-bridge systems under random excitations was established. The random excitations were analyzed and generated by the time series auto-regressive model from the experimentally measured wheel accelerations. The whole histories of the train running on bridges were simulated on computer. The responses of bridges were calculated and statistically studied. Based on the results, the reinforcement schemes for steel girders were designed and some of them were applied to real bridges. The field tests were carried out before and after the bridge reinforcement, which validated the effectiveness of the analytical method and the reasonability of the reinforcement schemes.