Abstract: Field tests on pile groups with prototype size have been carried out in order to study the behavior and the working properties of the cap-pile groups-soil interaction in the pile foundation. The soil reaction on the cap, the shaft resistance and the point resistance of pile have been measured by installing various measuring gauges. Based on the test results, the cap-pile groups-soil interaction characteristics were analyzed. In this particle, the regulations of the soil reaction on the cap, the shaft resistance and the point resistance of pile,and the mechanism of load transfer etc. have been analyzed and discussed with comparison to the result of a single pile.