The current analysis method for the main cable shape of a suspension bridge with a spatial cable plane involves solving complex differential equations for the main cable. However, this approach has certain drawbacks, such as the complicated form of constraint equations and the significant influence of initial values on iterative convergence. To address these issues and improve convergence in determining the main cable shape, the equivalent beam method was used, and geometric correlation equations between external loads and the main cable shape were derived. Subsequently, a two-stage analysis method was developed to solve the spatial main cable shape: During the rough calculation stage, decoupling processing minimized initial value requirements while obtaining accurate results with sufficient convergence. These results were then used as initial values in the precise calculation stage to iteratively calculate an exact solution for the spatial main cable shape. The feasibility and effectiveness of this two-stage analysis method were demonstrated through an example involving a pedestrian suspension bridge, and finite element software was used to verify the accuracy of calculation results. The research results demonstrate that the proposed method exhibits lower requirements for initial values and does not require the setting of initial values. The iterative process eliminates deformation compatibility conditions and stress-free length calculation, resulting in enhanced solving efficiency and rapid convergence towards obtaining an accurate solution for the main cable shape. This approach is suitable for analyzing the main cable shape of a single tower suspension bridge with a unilateral spatial cable plane.