This paper presents an evaluation for effectiveness of pre-dewatering on dynamic compaction for the reclaimed land built at near-shore. The Single-point Impact Test (SIT) and cone penetrometer are developed to perform the dynamic compaction under different water levels and drained conditions. The relationship between effective dynamic stress and cone resistance after impacts is presented. Dissipations of pore pressures measured in laboratory and filed are compared. Both cone resistances and improvement ratio in soils with higher water level are less than those with lower water level and in dry soils. The observations reveal that by lowering down the groundwater table prior to dynamic compaction in field, the soil resistances can be increased in depths and the depth of improvement could be extended.