Abstract: The suction caisson foundation is an important option for offshore wind turbines owing to its advantages of quick and convenient installation. With regard to the load characteristics of offshore wind turbines subjected to huge overturning moment loading, an approach for overturning bearing capacity of the mono-caisson based on deformation is proposed according to the model tests deformation mode and the soil-structure interaction of the mono-caisson foundation. The approach is different from the existing approaches for the ultimate bearing capacity. An approach for the overturning bearing capacity of multi-caisson foundations is also presented based on the multi-caisson model tests. The overturning bearing capacity of the mono-caisson is decided by the aspect ratio and the diameter, while that of the multi-caisson is depended on the diameter of the caisson and the spacing between the caissons. During a typical storm, the suction inside the caisson in silt is unable to dissipate. Thus its moment capacity can be analyzed as that under the undrained condition. The negative pressure will cause a substantial increase in the capacity of multi-caisson foundation against overturning moment. A typical wind turbine is taken as an example to carry out the calculation and design work utilizing the approaches mentioned above. This study can be a reference for similar real projects.