With an analysis of the types and formation mechanism of interferences in the vehicle-mounted ultra-wideband synthetic aperture radar (UWB SAR) detection system, a novel adaptive method is presented for the interferences suppression in the image domain based on the iterative technique. It can overcome the limitations and drawbacks of a batch processing method proposed by Tsaipei Wang. By exploiting the constant false alarm rate (CFAR) detector with weibull distribution, the new method can improve the accuracy of interference estimation. Then the parameters estimation and updating can be realized by using the iterative operation, and the adaptive interference suppression can be achieved on line. The processing results of real data show that the proposed method can effectively suppress the self-signature interference and is prone to real-time processing in structure. It can meet the needs of real-time preprocessing in the vehicle-mounted UWB SAR detection system.