Abstract：Ground vibrations induced by urban rail traffic are a major environmental concern in urban areas. In order to study the vertical vibration characteristics and its propagation behavior, an in situ test was carried out near the Line 13 of the Beijing Urban Railway between the Huilongguan Station and the Huoying Station. The responses of the free field ground were analyzed from three aspects as acceleration time histories, power spectra and vibration levels. Results show that the PGA of ground surface displays a pronounced attenuation with the increase of distance from track, while the vibration duration is somewhat prolonged. The dominant frequency ranges from 10Hz to 80Hz, whose lower band is primary for the points near track and upper band is primary for the ones further from track. The weighing VLz monotonic decay with distance, whereas at some frequency points close to natural frequencies of ground, the banded VLzs are amplified notably at certain distances. There is no significant change in the weighing VLz whether coaches are full or not. Comparing with InterCity railways, the urban rail traffic produces a more moderate ground vibration.