The mechanical performance calculation of submarine cables is one of the critical links in engineering construction. Based on analyzing the calculation method for the bending stiffness of AC single-core submarine cables with large cross-section cross-linked polyethylene insulation, taking a 500kV and 220kV submarine cable structure in China as an example, the composition of its bending stiffness was calculated The analysis showed that whether the outer sheath was made of copper wire armor, stainless steel sheath, or galvanized low-carbon steel wire, the overall bending stiffness of large cross-section submarine cables was determined. In the design of submarine cable engineering, Attention should be paid to the influence of the outer sheath material on the overall bending stiffness.