This paper concentrates on the data processing of Frequency Modulation Continuous Wave(FMCW),Synthetic Aperture Radar(SAR)in the case of wide swath and squint mode.In the mode,the Doppler centroid dramatically varies along slant range compared to conventional pulsed-SAR.This poses a challenge for system design and signal processing since a very large azimuth bandwidth would be introduced.In the paper,we accommodate the Doppler centroid variations with range by an improved spectral-length extension method,where a bulk range shift and updated Doppler centroid variations are introduced to greatly reduce the azimuth aliasing with respective to the existing methods.Moreover,an image formation approach that integrates wave number domain algorithm is presented to focus the raw data of FMCW SAR in the case of wide swath and squint mode.Point target simulation experiment demonstrates the advantages of the presented method. This paper concentrates on the data processing of Frequency Modulation Continuous Wave (FMCW), Synthetic Aperture Radar (SAR) in the case of wide swath and squint mode. In the mode, the Doppler centroid dramatically changes along slant range compared to conventional pulsed-SAR .This poses a challenge for system design and signal processing since a very large azimuth bandwidth would be introduced.In the paper, we accommodate the Doppler centroid variations with range by an improved spectral-length extension method, where a bulk range shift and updated Doppler centroid variations are introduced to greatly reduce the azimuth aliasing with may to the existing methods. Moreover, an image formation approach that integrates wave number domain algorithm is presented to focus the raw data of FMCW SAR in the case of wide swath and squint mode. point target simulation experiment demonstrates the advantages of the presented method.