Abstract: The semi-analytic method is adopted to analyze the influence of ground vibration due to train moving on viaduct supported by group piles to explore ways of reducing ground vibration. The semi-analytic numerical models include train-rail model, viaduct model and group pile model. The train is simulated by a multiple-mass spring-damping model. The America power spectrum is used to model the rail irregularities. The rail is modeled by Eular beam and the wheel-rail contact Hertzian non-linear formula is used. The wheel-rail force is solved by modal analysis method. The railway viaduct is modeled by elastically supported beam, and the impedance of group piles is analyzed by transfer coefficient matrix and interaction factors. The bridge pier-ground interaction force is solved by dynamic equilibrium equations and the ground vibration on half space is solved by Green function. The influence of the parameters of group piles on ground vibration is discussed. The results show that the rail irregularities have a great influence on pier force. The ground vibration greater than 6 Hz is influenced by the rail irregularities while the vibration less than 6 Hz is little affected. The ground vibration can be mitigated by combined bridge span and train speed. When the train speed is less than 260 km/h, the influence of pile diameter on ground vibration is limited; while it is greater than 260 km/h, increasing pile diameter can reduce the ground vibration. Increasing the pile spacing has two advantages of keeping away from the vibration increasing area and reducing the ground vibration as the increase of train speed. The increasing area of ground vibration can be reduced by the rational design of pile length.