The near-vertical backscatter characteristics of complex ground objects are one of the important factors affecting the echo waveform of radar altimeter. The measured data fitting method is adopted based on the parameter model to acquire the near-vertical backscattering coefficient, but it is only suitable for the ground and sea surface targets with flat terrain and relatively single medium. In this paper, with the mapping between Range-Doppler domain and geospatial domain, aiming to the simulation experiment data and the measured real data for airborne radar altimeter's Range-Doppler image of complex ground objects, a backscatter coefficient inversion algorithm is proposed and the obtained backscatter coefficients are quantitatively analyzed. It is verified that the proposed inversion algorithm has certain applicability and reference value.