The disclosure discloses an imaging method and device in a satellite-or-aircraft-borne (SAB) mobile bistatic Synthetic Aperture Radar (SAR), which includes: when an SAB mobile bistatic SAR starts imaging processing, a two-dimensional Fourier transformation is performed on a received echo signal to obtain a two-dimensional frequency domain echo signal; a radial phase of each range gate in the two-dimensional frequency domain echo signal is corrected using a radial-variable-slant-range frequency domain filter function; an orientation scaling Fourier transformation is performed on the two-dimensional frequency domain echo signal with the corrected radial phase to obtain a time domain echo signal; and each orientation correction is performed on the time domain echo signal using an orientation-variable-slant-range time domain filter function to obtain an image. With the disclosure, it is possible to countervail the dependence of the target on the slant range, thereby enabling better imaging accuracy.