The invention discloses a method for decomposing image four components of a polarization synthetic aperture radar and relates to analysis of the scattering characteristic of a polarization SAR image land object, in particular to a computing method of the scattering type of a building which has the non-zero orientation angle and is hard to process in an existing polarization SAR image decomposing method. As it is shown in the graph (1), the method includes the following steps that firstly, in terms of pixels corresponding to the building with the non-zero orientation angle in the image, a screening computing method is provided; secondly, in terms of the building with the non-zero orientation angle, a generalized even-time scattering model which can describe the scattering feature of the building is provided; thirdly, a non-negative feature value decomposing technology is provided for resolving the scattering components. By means of the method for decomposing the image four components of the polarization synthetic aperture radar, the defects of an original scattering model can be effectively avoided, a satisfying image decomposing result on the high-resolution full-polarized SAR image can be obtained and the method has the advantages of being novel, innovative, simple and practical.