Abstract: The design of surfaces with special curves is a classic topic in the field of CAD and has important applications in the optimization of free-form architectural surfaces. To address the challenges of high manufacturing costs for façades caused by the non-planarity of quadrilateral meshes and the inherent structural instability of quadrilateral gridshells in the design of free-form architectural structures, this paper proposes a surface optimization design method based on a hybrid diagonal mesh combining conjugate quadrilateral nets and geodesic quadrilateral nets. First, a model of the hybrid quadrilateral mesh is constructed, and an optimization algorithm combining geometric constraints with interactive design is presented to achieve efficient construction of the hybrid quadrilateral mesh. Then, according to the specific design requirements of freeform architectural surfaces, a comprehensive design scheme is provided, including initial mesh generation, interactive form adjustment, and structural form design. Based on the above method, three surface roof design cases were constructed. Case analysis results show that the proposed method not only ensures the planarity of façade units, but also significantly improves structural stability through optimization of the geodesic diagonal cable layout. This method combines geometric accuracy with engineering feasibility, providing a solution for lightweight and low-cost design of large, complex freeform architectural surfaces.