The accuracy of the traditional ω-k algorithm of Frequency Modulated Continuous Wave (FMCW) Circular Synthetic Aperture Radar (CSAR) for image interpolation when reconstructing the cylinder areas has direct influence on the quality of imaging, and the process needs a large amount of calculation.To solve the problem, an ω-k algorithm based on Nonuniform Fast Fourier Transformation (NUFFT) is proposed, by which the echo signal of wave-number domain is deduced according to the fourth order Taylor expansion based on the slant range from radar to target.On the basis of which, the two-dimensional NUFFT is used instead of the interpolation function, and implements focused imaging.