Abstract: This paper proposes a radar cross section （RCS） test method based on spherical aperture synthetic imaging， establishes an echo signal model based on decoherence function， and derives an RCS inversion method based on spherical aperture synthetic imaging. First， all the azimuth-pitch scattering information of the measured target is obtained through the spherical aperture synthetic three-dimensional imaging method； Second， the three-dimensional single looking complex （SLC） image of the target is obtained by three-dimensional wavenumber domain integral imaging processing method of improved decoherence function， the information of interference target is suppressed by image spatial filtering； Finally， the RCS of the target is inverted through wavenumber domain transformation. This paper introduces the decoherence function to effectively suppresses the effects of angle decoherence and frequency domain decoherence on imaging and RCS inversion， the conclusion of the method characterizes the amplitude characteristic and phase characteristic of the RCS of the target in the azimuth-pitch direction， theoretical deduction， simulation experiment and numerical analysis verify the correctness and effectiveness of the method in this paper.