Abstract: Based on the field model tests on a pile group in soft soil,the cap-pile-soil interaction behaviour was analyzed.It was indicated that lateral friction of the pile group and soil reaction beneath the pile cap increased with the in crease of pile spacing,and the point resistance increased with the decrease of pile spacing the compared with single pile.When the pile spacing increased to 6d,the lateral friction of the pile group tended to equal to that of single pile,but the point resistance of pile group was still larger than that of single pile.The soil reaction beneath the pile cap increased with the increase of the pile spacing,and when the pile spacing increased to 6d,the soil reaction beneath the pile cap only developed 50% which was less than that of other kinds of soil.The settlement of the pile group with large pile spacing was mainly caused by pile punching and soil compression beneath the pile cap,obviously defferent form block deformation of pile groups with small pile spacing.Based on the above-mentioned characteristics of the pile group with large pile spacing,a simple design method for composite foundation with settlement-reducing piles was proposed to calculate compression of soil beneath the pile cap and pile-soil interaction in order to obtain the settlement of composite pile foundation.The proposed method had been verified with more than ten practical engineering projects.