Abstract: We develop an originally experiential methodology to retrieve bare soil moisture by synthetic aperture radar(SAR).The model does not require any field measurements to support,and only requires the two different kinds of polarized backscattering coefficient data.Taking into account both of the roughness parameters RMS S and the correlative length L,we combine the two roughness parameters and introduce a new roughness parameter(Rs=S3/L2)into this model.Hence,the unknown parameter in the model reduces to Rs and the volume of soil water content mv.Then,the ground soil moisture can be retrieved by integrating the equations of VV and VH polarization.The simulating data was used to validate the accuracy of this model.The result shows that there is a strong linear relationship(R2>0.71)when the incidence angle is not very small(θ0>20°).The inversion model can get a better accuracy of soil moisture without any measurements of surface roughness.This method is especially effective in the area with complex terrain where the surface roughness is difficult to be precisely measured.