Aimed at the shortcomings of the segmental catenary method, such as poor convergence performance and low computational efficiency, this paper proposes a coordinate system method based on overall mechanical analysis (COM). In this method, the initial cable shape is assumed to be linear and the target cable shape is then calculated by iterations based on the overall equilibriums of forces. This method is used to calculate the cable shape of the Chishui Bay Bridge in Hebei Province by MATLAB, and the results are compared with measured data. The comparison shows that the proposed method has a faster convergence speed and higher accuracy.