•Form finding and optimization method for flexible-supported cable nets is proposed.•The interactive effect is captured by solving the non-compatibility problem.•Linear form for the determination of free node coordinates is derived.•The method is applied to mesh reflector antennas to demonstrate the efficiency. Cable network structures consist of the cable networks and supporting frames, and the whole structures form the equilibrium states under the interactions between them. The existing methods haven’t considered the flexibility of the supporting frames and thus fail to fully capture the interactive effect between cable networks and flexible frames in the design optimization. This leads to the deviations between the design results and the real equilibrium states. Here we propose a form finding and design optimization approach for cable network structures with flexible frames. By solving the non-compatibility problem between cable and beam elements (due to rotation DOF), the cable network and supporting frame can be coupled to accurately model the real equilibrium state in the optimization model. We also derive the linear form for the determination of the free node coordinates from systematic equilibrium equations, which greatly reduces the computing cost of the optimization design and makes the multi-variable optimization more achievable. The proposed approach is effective for the form finding and design optimization of flexible supported cable networks with high surface accuracy requirements and multiple design variables. It is applied to mesh reflector antennas, and case studies are provided to verify the effectiveness of the methodology.