To study the ground vibration induced by high-speed trains across bridges, a field test was carried out in vicinity of a simply supported box-girder with a span of 32 m on Tianjin-Qinhuangdao railway line. Ground vibrations in the longitudinal, lateral and vertical directions were measured with train speeds in the range 250-385 km/h. The test data were analyzed in both time and frequency domains. The results show that cyclical peaks of acceleration can be clearly distinguished in the near field, and the excitation frequencies of wheelbase and the adjacent bogie space of the front and rear cars make the main contributions. The dominant frequency of ground vibration in the three directions is 25-80 Hz, and the vertical ground vibration attenuates mainly in the dominant frequency band; however, the longitudinal and lateral ground vibrations obviously attenuate in 1-80 Hz. For all test train speeds and all test points, the vertical ground vibrations are stronger than the longitudinal and lateral ground vibrations, and the maximum difference of vibration acceleration levels (VALs) between the longitudinal and lateral ground vibrations is about 2 dB. A phenomenon of amplification for the longitudinal and lateral ground vibrations is observed at the distance of about 30 m. Overall VAL of the near field increases about 6 dB when the train speeds increases from 250 to 320 km/h. However, the differences of overall VALs at all locations are less than 2 dB while speeds in the range of 330-385 km/h.