In view of the fact that in the design of the main cable, the high safety factor is used to avoid the detailed secondary stress analysis and the bearing capacity of the main cable is not fully utilized, a more detailed analysis of the secondary stress of the suspension bridge is attempted. The secondary stress of the main cable of the suspension bridge due to the difference in wire strand length, the elastic modulus of steel wire and the bending of steel wire was analyzed, and the corresponding empirical calculation formula was given. The secondary stress caused by the change of cable angle is analyzed by the previous calculation method, and the theoretical analysis and formula derivation are carried out for more general situations, and the calculation algorithm is given. The secondary stress caused by the change of cable shape is decomposed into three parts: porosity difference, cross-section characteristic difference, and cross-section shape difference. The secondary stress caused by the circular section of the main cable out of the main saddle to the circular section of the first cable clamp was analyzed. Finally, combined with the example of calculating the secondary stress of the main cable of a long-span suspension bridge in China, the occurrence of the secondary stress and the influence of the secondary stress on the structural safety are analyzed, and the safety factor of the case is analyzed according to the calculation method of the main cable of the long-span suspension bridge in the United Kingdom, Japan and Denmark, and its safety can be guaranteed.