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The geomorphic features of alluvial fans in arid and semi-arid areas,affected by tectonic and climatic changes,could provide abundant valuable information for studying paleoclimatic and paleoenvironmental changes.Synthetic aperture radar (SAR) remote sensing technology has already been the key spatial observation tool to extract the surface features of alluvial fans.In this paper,the surface roughness parameter of Shule River alluvial fan was extracted from RadarSat-2 C-band data,therefore the roughness characteristics with different alluvial fan units obtained also from the RadarSat-2 polarimetric data were analysed.According to this study,we try to solve the following two problems.1) Developing a roughness inversion method which is more suitable for the surface of alluvial fans in arid and semi-arid areas.Considering the existing SAR backscattering models can hardly obtain good roughness results in arid areas due to the overestimated moisture parameter.A dielectric constant fixed strategy is used to improve the inversion accuracy of roughness parameter in the arid surface of alluvial fans.2) Researching the surface roughness parameter characteristics of the Shule River alluvial fan units with different ages,and understanding the relationship between the surface geomorphic features of alluvial fans and the paleoenvironment.