Abstract: An important cause for the practical settlement of some embankments with rigid-pile composite foundation larger than calculated settlement is the severe serious defects of the existing methods for settlement calculation. The superimposed stress method is proposed for calculating the settlement of a rigid-pile composite foundation under embankment by analyzing the differential settlements and interactions between piles and soils. The settlement of the composite foundation is gotten by the layer-wise summation method after the superimposed stresses of piles and soils among piles are calculated based on the analysis of interactions between piles and soils. The proposed method validated by a practical project is applied to investigate the influences of length, distance, enlarged base and cap of rigid piles on the settlements of composite foundation of embankment. The settlements calculated by the proposed method and the existing methods are compared. It is proven that the bearing capacity of piles, load transferred to piles by pile cap, interaction between piles and soils can be taken into account by the proposed method, and the calculated settlement is close to the practical settlement. The pile cap which transfers most embankment load to the piles can decrease settlement prominently. The under-reamed pile is more economical and reasonable than the length-increasing pile. The composite foundation consisting of sparse strong piles with large caps is more economical and reasonable than the composite foundation consisting of dense piles.