Abstract: In this paper a concept of Huge Flexible Stewart Platform is presented for the suspending cable structure of large spherical radio telescope′s feed system, and the definition of its solution space is also made through feed cabin′s nonlinear static balance equation. There exist 6 plains on which 6-cable huge flexible Stewart platform′s solution space equals zero, so a continuous and stable space scanning of feed cabin can not be guaranteed. Based on the consideration of feed cabin′s running principle and forces on cables, 8-cable huge flexible Stewart platform is designed by adding 2 more pull-down redundant cables. Solution space′s calculation result demonstrates that 8-cable huge flexible Stewart platform not only erase those position that solution space are zero, but also increase feed cabin′s working angle. The study in this paper provides theoretical basis and valuable data for FAST not using 6-cable but 8-cable huge flexible Stewart platform.