Offshore wind energy is one of the most important clean energy sources developing in China in recent years. As a new type of offshore wind turbine foundation, the wide-shallow bucket foundation with large diameter has a good ability to withstand moments. It is thus suitable for offshore region in China with soft clay deposits. Moreover, this type of foundation has advantages of onshore prefabrication, foundation-tower-turbine integrated floating transportation and suction installation, resulting in a good benefit for cost reduction. To better understand the bearing capacity of the wide-shallow bucket foundation in clay, numerical analyses are conducted to study the monotonic ultimate bearing behavior. The horizontal and moment ultimate bearing capacities and corresponding failure mechanisms are obtained. By building the velocity field based on the failure mechanisms of the bucket foundations, combined with the virtual work equation and the internal energy loss rate function, the upper bound solutions for the horizontal and moment ultimate bearing capacities of the bucket foundations are established and programmed using mathematical software. The results of the upper bound limit analysis have a good agreement with the calculation of the numerical analyses.