There is a growing interest in the frequency modulated continuous wave (FM-CW) SAR for its advantages such as small cubage, light weight, cost-effective and high resolution. In this paper, imaging process in range direction was analyzed in detail, and a useful conclusion was drawn that the RVP is removed in the course of performing Fourier transform in range direction; Then, the factors affecting range resolution for the de-chirped FM-CW SAR was discussed，and the method improving the range resolution as well as decreasing the range sample frequency was put forward. The deduction of the process shows that the slope factor exists in FM-CW SAR. Therefore, the generation of the slope factor and the method of de-sloping were analyzed, and the corresponding range imaging algorithm was also presented, creating better focus conditions for the azimuth direction.