Based on discrete Fourier transform theory and the time domain and frequency domain analysis on a great deal of field test data of the bridge(culvert)subgrade transition section on Qin-Shen High-speed Railway

vibrtion acceleration amplitude spectrum and power spectrum and phase spectrum of the top surface layer of the subgrade

and the relationship between vibration first frequency of the top surface layer of the subgrade and vehicle velocity are acquired. The dynamic responses of subgrade-bridge transition section under high-speed train action are tested in Qin-Shen Railway. The longitudinal distributive regularities of dynamic responses of the transition section

relationships between train speed or axes weight and dynamic stress and variation of dynamic stress with depth are analyzed. The test provides important basis for the design and construction of the transition section roadbed of high-speed railways.