Secondary electromagnetic polarimetric scattering from a barchan dune is studied. The secondary polarimetric scattering field from the secondary scattering facet is deduced in the Kirchhoff approximation with the waves reflecting from the first scattering facet based on the Ray-tracing theory. The results show that secondary scattering plays an important role in specific range of angle. The co-polarized backscattering coefficients of the lee slope have a local peak value when the incident angle equals the repose angle. Cross-polarized bistatic coefficient of the lee slope near the backscattering region is enhanced when the incident angle is close to the repose angle. The secondary polarimetric scattering between two dunes in line is especially noticeable. The information about wind field in desert region can be retrieved and analyzed by the results in this paper.