Abstract: In order to solve the main problems of the breakwater with cylindrical foundation, a new type of deepwater breakwater named circular and rectangular suction deepwater breakwater was proposed. According to the undrained cyclic triaxial test data of Tianjin marine soft soil, the calculation formula of cyclic strength of soil element was deduced. An efficient calculation method for cyclic capacities of circular and rectangular suction breakwater was established by combining the concept of cyclic strength with the failure envelope theory of bearing capacity. It is concluded that the size of the failure envelope of cyclic capacities for circular and rectangular suction breakwater gradually expands with the increase of the depth-to-diameter ratio of the foundation while it first expands outward and then shrinks inward with the increase of the vertical load. When the vertical load is small, the failure envelope considering the cyclic softening effect of the soft soil is significantly smaller than that without considering the cyclic softening effect.