T-matrix method was employed to analyze the relation between the co-polarization phase difference of back scattering of vegetation and its geometrical and physical parameters, and the effect from the frequency and the incident angle of radar based on this kind of relation. The results showed that the phase difference is affected by the geometrical parameters (such as the shape, the growth state of wattle and leafage etc.) and the physical parameters (such as the real part and the imaginary part of the dielectric constant etc.) in different ways. In addition, the frequency and the incident angle of radar have heavy effect on the results. All of these are significant in assorting crop and monitoring vegetation. T-matrix method was employed to analyze the relation between the co-polarization phase difference of back scattering of vegetation and its geometrical and physical parameters, and the effect from the frequency and the incident angle of radar based on this kind of relation. showed that the phase difference is affected by the geometrical parameters (such as the shape, the growth state of wattle and leafage etc.) and the physical parameters (such as the real part and the imaginary part of the dielectric constant etc.) in different In addition, the frequency and the incident angle of radar of heavy effect on the results. All of these are significant in assorting crop and monitoring vegetation.