The work aims to design a flexible broadband metamaterial absorber for electromagnetic stealth in the 2~18 GHz frequency band. The impedance matching and absorbing mechanism and polarization sensitivity of the absorber were analyzed by combination of equivalent circuit and full wave simulation, and the absorber was tested and verified after the frequency selective surfaces were fabricated on organic materials with conductive ink. With a total thickness of 14.6 mm, the absorber demonstrated an absorption rate of above 90% and a relative bandwidth of 160.8% in the 1.97~18.15 GHz range, covering the S, C, X, and Ku bands. This absorber showed excellent electromagnetic stealth performance, including polarization insensitivity, conformal with stealth targets, and reduction in radar cross section. The results from combination of circuit and field analysis are consistent with experiments, and this absorber exhibits potential applications in electromagnetic stealth technology within the 2~18 GHz frequency band.