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With the rapid development of high-speed railway, special areas such as transition zones have attracted increasing attention. To analyze dynamic responses of subgrade bed in the culvert-embankment transition zone, field tests were carried out on the Beijing-Guangzhou high-speed railway in China. The field instrumentation data undergone a series of signal processing operations were classified by train running conditions. The amplitude and frequency characteristics of dynamic responses were then analyzed comprehensively. The synergistic influences of train speed, culvert approaching/departing, and axle load were discussed. It was found that the abrupt change in track supporting condition caused longitudinal fluctuation of dynamic displacement responses, and the dynamic stress responses in the longitudinal direction resembled the "V" shape. The culvert approaching/departing exerted a significant influence on the longitudinal distribution of dynamic displacement responses, which exhibited a linearly ascending trend with increasing train speed. The influence of increasing train speed on dynamic stress responses attenuated rapidly with increasing depth. The dominant frequencies of subgrade bed were more significantly related to train geometry rather than track and substructure geometry, and the dominant frequencies were particularly affected by the periodic excitation frequency associated with the railcar length. The proportion of frequency components within 80 Hz became greater as the longitudinal distance away from the culvert increased. The dynamic stress responses were more sensitive to axle load than train speed. The dynamic displacement responses were more significantly affected by train speed than axle load for train speed exceeding beyond about 260 km/h. The findings of this study could provide technical reference for long-term operation and maintenance of high-speed railway track in transition zones. • Field investigation of dynamic responses of subgrade bed at non-ballasted railway culvert-embankment transition zone. • Comprehensively analysis of amplitude and frequency characteristics of dynamic responses. • The synergistic influences of train speed, running direction, and axle load on dynamic responses. • The vibration frequency characteristics of subgrade bed highly related to geometry features of train and track. [ABSTRACT FROM AUTHOR]