Taking into account the influence of saddle on the length of main cable and considering the convenience of operation as well as the calculation accuracy, an analytical calculation method for the length of main cable at the saddle of long-span suspension bridge was proposed. First, according to the geometric relationship between the main cable and the saddle, the main cable curve correction algorithm was derived. Then, the Newton-Raphson iterative method was used to solve the obtained binary nonlinear equations. Finally, the reliability of the method was verified using main cable saddle and loose cable saddle as examples. Results show that compared with traditional algorithm, six equations and six initial input parameters were reduced, which made the expression form clearer. Only two parameters were needed to be input and there was no strict requirement for the setting of the initial values of the parameters, which led to fast convergence and thus enhanced the operability. The number of iterations was reduced by 50%, and the calculation time was less than 10% of the traditional algorithm, which greatly improved the calculation efficiency and met the engineering requirements. The algorithm proposed in this paper can be easily applied to the determination of the length of main cable curve and the position of cable saddle during construction, which can make the construction control of the long-span suspension bridge more accurate so as to ensure that the state of the accomplished bridge meets the design requirements.