To study the vibration induced by elevated-road traffic and its propagation rules in soil, field measurements were carried out in different sites. Large numbers of statistics indicate that: the ground vibration induced byelevated road traffic is vertical vibration primarily, whose dominant frequency ranges from 5 to 25 Hz. The vertical vibration do not always attenuate exponentially with the increasing distance from the vibration source to the measurement location,for there is a vibration amplified region at a certain distance and the horizontal vibration intensity follows a sinedistribution. The ground vibration is related to multi factors as the vehicle load, the vehicle velocity, the international roughness index(IRI) of the road, the expansion joint, the basement form, the soil dynamic performance, the wave cross section and the vibration reduction methods. The combination function method which could reflect the effect of the vibration amplified region and other multi factors was proposed to forecast the Z-direction vibration levels. The relevant forecast fomula for Z vibration levels was given, which had a better fitting effect than the conventional methods.