Abstract: The researches on the prediction of cyclic lateral cumulative deformation of pile foundation for offshore wind turbines mainly focus on the characteristics of external cyclic loading, ignoring the influences of pile-soil relative stiffness. A series of 1g model tests are carried out on sand by the self-developed cyclic loading system. The test results show that the normalized cumulative deformation y_N/y₁ increases exponentially with the increase of the cycle number N, and increases with the increase of the cycle load ratio ζ_c, but it is not significantly correlated with the cycle amplitude ζ_b. Also, the relationship between the pile-soil relative stiffness and the normalized cumulative deformation shows a "s" shape, that is, the pile-soil relative stiffness has small effects on the cumulative deformation of the flexible and rigid piles. But, the cumulative deformation of the semi-rigid pile increases with the increasing pile-soil relative stiffness. On this basis, the prediction model for the cyclic lateral cumulative deformation considering the combined effects of characteristics of cyclic loading and pile-soil relative stiffness is proposed. The rationality and reliability of this method are verified by comparing with the experimental data in the literatures.