The improvement of the train operation speed will increase roadbed vibration, and undermine its dynamic stability, and may cause great subsequent settlement; when it reaches the limit value, the roadbed structure will get a bulking failure. Therefore, the dynamic response and disastrous mechanism of subgrade structure under high-speed train load has become an international and urgent research subject in the process of high-speed railway construction and operation. Relying on Wuhan inter-city typical engineering, a large-scale model test of vibration due to train load is carried out by using a self-developed excitation system. By simulating the process of loading with vibration exciter, the time history curve of velocity and the space distribution features of different subgrade layers under the action of different frequencies of vibration force is obtained; and then the velocity transfer and attenuation law of subgrade under the train load is revealed. The experiment results show that. The curve of velocity on subgrade structure has a obvious cyclical peak under different frequencies of vibration force; the speed amplitude on subgrade structure will ever-reduce along the depth direction and show a trend of exponential decay under frequencies of vibration force. The research results will provide a certain reference for designing, construction and operation of practical engineering.