Abstract: Dynamic compaction is one of the common methods for site improvement.But the influence zone of dynamic compaction often can not be estimated well,which has become a problem restricting the wide application of the method.This paper examines thefield measured data during the site improvement with the dynamic compaction at a harbor.,The influence zone in the ground in terms of the depth and horizontal distance is presented from the field monitored data.The monitored data include the ground vibration displacements,velocity and acceleration at different depths and distances during the impacting of the hammer.The vibration displacement,velocity,and acceleration against the depth and distance are plotted as the attenuation curves for the assessment.of the tamping.