Aiming at the drawbacks of the traditional imaging algorithm for circular Synthetic Aperture Radar (SAR)，such as limited resolution，high sidelobes，and low imaging quality，a three-dimensional imaging algorithm for circular SAR combining Fractional Fourier Transform (FrFT) with Orthogonal Matching Pursuit (OMP) algorithm is proposed.First，the echo model of circular SAR is established.After selecting an excellent imaging algorithm，the energy concentration characteristics of Linear Frequency Modulation (LFM) signals in the fractional Fourier domain are utilized.The FrFT is employed for pulse compression to improve the resolution in the range direction.Then，based on the sparse properties of circular SAR signals，the OMP algorithm is used to estimate the azimuth and elevation angles of the signals in each range cell，achieving high-resolution imaging with a small amount of data.The simulation results show that: 1) The peak sidelobe ratio in the range dimension is 14% lower than that of the Iterative Adaptive Approach (IAA) algorithm and 13% lower than that of the OMP algorithm;and 2) In the angular dimension，it is 4% lower than that of the IAA algorithm.