Light-weight radar absorbing material (RAM) based on resistive frequency selective surfaces (FSS) was designed and prepared. The principle of the resonances of the RAM was analyzed by calculating the impedance of the FSS and the grounded substrate according to the equivalent circuit method, and the results show that a wideband absorbing structure can be gained by producing two adjacent resonances. After design and optimization by Genetic Algorithm (GA), the RAM with absorbing bandwidth of 7.5~18GHz below -10dB was obtained, whose thickness is only 3mm. The designed RAM was gained by preparing resistive patches on the grounded dielectric substrate of rigid polyurethane foam using screen painting technology. The density of the absorber is only 0.2g/cm3, the reflectivity was measured and it shows that the experimental result is consistent with the design one.