Based on Abaqus quasi-static analysis method for the cargo hold area structure of Floating Production Storage and Offloading (FPSO) main hull, a three-step strong frame model is established to study its ultimate bearing capacity under vertical bending moment and 30° bow wave, considering the material nonlinearity and actual sea conditions in the working area of the FPSO. The relationship between the vertical load and horizontal load in the combined load is determined by the response amplitude operator ratio of bending moment directly calculated by the whole ship wave. The results show that: the resistance ability of the structure to mid-arch bending moment is stronger when the structure is subjected to vertical load; when horizontal load is introduced, the resistance ability of the structure to vertical external load is reduced, and the influence on the mid-vertical extremely high bending moment is greater, when the ultimate bending moment occurs, the corresponding structure generally suffers buckling failure in a large area; the horizontal ultimate moment always appears before the vertical ultimate moment; the bilge structure effectively transits the combined load between the middle arch and the horizontal moment.