The invention discloses a method for identifying internal force of a main cable of a large-span suspension bridge, and relates to the technical field of maintenance of the main cable of the suspensionbridge. The method comprises the following steps: acquiring an unstressed radial load set q per unit length, an equivalent elastic modulus E of a main cable strand, a net area A of the main cable, acable force Pi of a sling, and vertical and longitudinal relative coordinates of a lifting point during blanking of the main cable; Due to the fact that the bending rigidity of the cable is very small, and no fixed shape exists, for cable structure calculation of the suspension bridge, the following assumptions can be adopted: (1) the cable is ideal and flexible, cannot resist pressure, and cannotresist bending; 2, the cable material conforms to Hooke's law; And (3) the acting direction of the cable unit load and the cable curve are in the same vertical plane. By deducing the relationship between the internal force of the main cable and the structure system parameters, the internal force of the bridging main cable can be accurately obtained only by actually measuring the structure systemparameters of the main cable, and the problem that the internal force of the main cable of the existing large-span suspension bridge is huge and inconvenient to identify is solved.