Focusing on the problem of the space-variance of the range cell migration term for bistatic Synthetic Aperture Radar (SAR), a Scaled Inverse Fourier Transform (SIFT) based imaging algorithm for constant-offset configuration bistatic SAR data processing is proposed in this article. Range cell migration correction is realized through two times phase multiplies and one time convolution operation. Since the imaging algorithm is based on an exact precise spectrum which is deduced from the Geometry-Based Formula (GBF) algorithm, the proposed algorithm can handle the bistatic SAR data which are obtained with a large baseline to ratio. The advantages and effectiveness of the proposed imaging method have been verified by simulated and comparable experiments. Moreover, unlike the other scaling imaging algorithms which are dependent on the frequency modulated characteristics of the signal, the SIFT imaging algorithm is also suitable for phase-coded signal, which has a wider application areas.