The invention belongs to an imaging method for nonlinear frequency modulation label change in the synthetic aperture radar imaging technology, which comprises the steps of two-dimensional frequency domain unfolding, filtering processing, nonlinear frequency modulation label change, distance compression, distance migration correction, rest phase compensation and position compression. In the method of the invention, the characteristics of orthogonality and minimum square error of the Legendre polynomials are utilized for carrying out three-order unfolding on the two-dimensional frequency domain signals of the obtained echo signals according to the Legendre orthogonality polynomials, and then, the focusing imaging on targets is realized through carrying out filtering processing and the like on three-order phase items in echo signal two-dimensional frequency domain expression. When the method of the invention is adopted, the maximum phase error under the same condition is less than 0.2 percent of the maximum phase error in the prior art, so the assurance is provided for the high-precision imaging under the large-inclination view angle condition. Therefore, the method of the invention has the characteristics that the phase error in the imaging process can be effectively reduced, the imaging processing of the large-inclination view angle is realized, in addition, the imaging effect is good, the imaging processing efficiency and the precision are high, and the like.