Abstract: Large-diameter pile foundations are more and more widely used in ocean engineering. The current p-ycurve approach given in the API code cannot be used for large-diameter piles subjected to lateral loads. To deal with this problem, the behaviors of large-diameter piles in sand under lateral static and cyclic loadings are investigated based on several centrifugal model tests. The calculation approach for lateral displacement of pile shaft and soil reaction force using the measured bending moment of the pile shaft is verified. Static p-ycurves of large-diameter piles in both dry and saturated sands are also obtained. By modifying the initial stiffness of p-ycurves, a series of hyperbolic p-ycurves are adopted to compute internal force and deformation of large-diameter piles. The change of deformation and internal force of large-diameter pile foundations under one-way cyclic loading is released. The test results show that the head displacement and the maximum moment of pile shaft almost linearly increase logarithmically with number of cycles. Finally the cyclic p-ycurves of large-diameter pile foundations according to bending moment of the pile shaft in each cycle are obtained. A cyclic degradation factor related to the cyclic stress ratio and a corresponding approach for analyzing cyclic deformation and internal force of the pile shaft are proposed.