In this paper, bi-spectrum estimation method is adopted. Based on non-Gaussian AR-model, parametric bi-spectrum method is used to extrapolate radar echo signal; then the ISAR imaging has been done. Simulation and real data experiment result show that the method adopted in this paper dramatically improves the ISAR imaging resolution as compared with the traditional FFT method. Furthermore, less calculation is able to meet the needs of real-time or half-real-time ISAR imaging.