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In this paper, ultra-wideband and wide-angle radar cross section (RCS) reduction of a concave structure is designed and realized based on a chessboard polarization conversion metasurface (CPCM), employing an ultra-wideband polarization conversion metasurface (PCM) composed of a single layer of square split-ring resonators. The concave structure, which is equivalent to an octagonal-like prism, is divided into eight regions. To achieve perfect phase cancellation in the non-central region, it can be equivalent to oblique incidence when the central region is under normal incidence, and phase compensation of the unit cell of metasurfaces in the non-central region is considered. The simulated results demonstrate that the RCS reduction of the proposed concave structure is less than −10 dB in the frequency ranges of 8.8 GHz to 35.75 GHz with fractional bandwidths of 120.99% and exceeds −30 dB at numerous resonant frequencies such as 9.52 GHz, 13.89 GHz, 23.45 GHz, and 35.2 GHz under normal incidence. The experimental results are in good agreement with the simulations. Furthermore, the RCS reduction characteristics of the proposed concave structure at different azimuth angles are also evaluated. Numerical calculations and experiments show that the wide-angle RCS reduction from 0° to 34° is achieved. To the best of the information we have, this is the first time that the chessboard metasurfaces, which consist of several polarizing reflectors, have been employed to obtain broadband and wide-angle RCS reduction for the concave structure. This technique validates the novelty and effectiveness of wide-angle and ultra-wideband RCS reduction of the concave structure. [ABSTRACT FROM AUTHOR]