In this work, the effect of the surrounding soil condition on the fundamental modal characteristics and dynamic response of railway bridges with integral abutments is studied. Due to the computational cost of the full FE models and the lack of reliable simplified models, the effect of the soil-structure interaction is usually neglected in the vibration analysis of the high-speed railway bridges. In the present study, an efficient simplified numerical model is employed to evaluate the modal characteristics of the railway bridge-soil systems. After verifying the accuracy of the simplified numerical model against rigorous models, the effect of the span length and abutment/soil stiffness on the dynamic response of the studied bridges is investigated through a comprehensive parametric study. Several case studies which covers different span lengths and abutment conditions are chosen. It is shown that the SSI has substantial effect on the dynamic response of the short and stiff bridges while its effect decreases as the ratio between the deck stiffness and the abutment/soil stiffness decreases. The results may lead to review the recommended modal damping ratios for this type of bridges in the code provisions and design manuals.