To reduce the surface deformation of a remote sensor reflector in complex and execrable space environments, a flexible support structure was designed. By defining the thickness, width and radius as design variables, the flexible hinge in an oblong reflector subassembly was optimized. Then,the surface figure precision, structural strength and dynamic stiffness of the reflector subassembly in the thermal-structural coupling state were analyzed with finite element method. Simulation results show that the maximum PV value is decreased to 59.03 nm from 350.08 nm, the maximum RMS value is decreased to 9.11 nm from 102.67 nm and the thermal dimensional stability is ensured by proposed flexible structure. Finally, the thermal-structural simulation subassembly was subject to a mechanical test,and results indicate that the fundamental frequencies of the component in three directions are 264 Hz, 290 Hz and 320 Hz,respectively. Analysis and test results demonstrate that the flexible support structure is reasonable.