A rectangular reflector for a space remote sensor is designed in detail by taking the choice of material, the lightweight of the reflector and the design of the supporting structure into account. The reflector uses a flexible supporting structure which has an open bottom and a low weight triangular reinforced six-point backside structure. The parameters of the flexible supporting structure are determined with a finite element analysis technique. Finally, the dynamic characteristics of a reflector assembly prototype are tested in a mechanical test environment. The test result shows that this structure meets the design requirement.