Conventional Frequency Scaling (FS) algorithm is applied to process Frequency Modulated Continuous Wave (FMCW) SAR, which will lead a heavy range frequency aliasing. Through analyzing basic principle of the FS algorithm and combining the scaling propertation of the Fourier transform, with the presence of a constant factor, this paper proposed a improved frequency scaling algorithm for range anti-aliasing. The proposed algorithm holds performance of the conventation one and just removes the aliasing. The successfully imaging a point target shows the validity of the proposed method.