An imaging method for a Synthetic Aperture Radar in a high squint mode, wherein imaging step comprises: Step 1: performing azimuth Fourier transform for high squint SAR echo original data to obtain echo signals in azimuth Doppler domain-range time domain; Step 2: utilizing a high squint SAR echo signal time domain model, a spectrum model and a time domain and frequency domain mapping relation to multiply the echo signals in the azimuth Doppler domain-range time domain by a perturbation function to eliminate the dependence of an echo signal quadratic azimuth-range coupling factor on change of a target slant range, and obtain an echo signal having a first-order range-azimuth coupling relation with the target slant range, the range cell migration of the echo signal is expressed by a brand new range migration factor; Step 3: performing range Fourier transform for the obtained echo signal having the first-order range-azimuth coupling relation with the target slant range to obtain a two-dimensional spectrum which is an echo signal having the first-order range-azimuth coupling relation with the target slant range; Step 4: multiplying the two-dimensional spectrum by a reference function; the reference function is a conjugate function of a point target echo spectrum at a reference slant range; therefore, the two-dimensional spectrum is multiplied by the reference function to compensate all phases, which do not vary with the range, of the two-dimensional spectrum to obtain a signal differential range migration spectrum; Step 5: constructing a range migration expansion factor according to characteristics of signal differential range migration spectrum, rectifying a differential range migration factor of the echo signal in the two-dimensional frequency domain by utilizing Chirp-Z transform, and completing range migration rectification by performing convolution once and phase multiplication twice to obtain a range-compressed signal; Step 6: performing phase multiplication for the range-compressed signal through the azimuth to compensate an azimuth residual phase, performing azimuth compression for the range-compressed signal and obtaining an azimuth-compressed signal; Step 7: performing azimuth inverse Fourier transform for the azimuth-compressed signal to obtain a focused SAR image. Step 1: performing azimuth Fourier transform for high squint SAR echo original data to obtain echo signals in azimuth Doppler domain-range time domain; Step 2: utilizing a high squint SAR echo signal time domain model, a spectrum model and a time domain and frequency domain mapping relation to multiply the echo signals in the azimuth Doppler domain-range time domain by a perturbation function to eliminate the dependence of an echo signal quadratic azimuth-range coupling factor on change of a target slant range, and obtain an echo signal having a first-order range-azimuth coupling relation with the target slant range, the range cell migration of the echo signal is expressed by a brand new range migration factor; Step 3: performing range Fourier transform for the obtained echo signal having the first-order range-azimuth coupling relation with the target slant range to obtain a two-dimensional spectrum which is an echo signal having the first-order range-azimuth coupling relation with the target slant range; Step 4: multiplying the two-dimensional spectrum by a reference function; the reference function is a conjugate function of a point target echo spectrum at a reference slant range; therefore, the two-dimensional spectrum is multiplied by the reference function to compensate all phases, which do not vary with the range, of the two-dimensional spectrum to obtain a signal differential range migration spectrum; Step 5: constructing a range migration expansion factor according to characteristics of signal differential range migration spectrum, rectifying a differential range migration factor of the echo signal in the two-dimensional frequency domain by utilizing Chirp-Z transform, and completing range migration rectification by performing convolution once and phase multiplication twice to obtain a range-compressed signal; Step 6: performing phase multiplication for the range-compressed signal through the azimuth to compensate an azimuth residual phase, performing azimuth compression for the range-compressed signal and obtaining an azimuth-compressed signal; Step 7: performing azimuth inverse Fourier transform for the azimuth-compressed signal to obtain a focused SAR image.