Abstract: Along track interferometry (ATI) is an easy and efficient method to detect ground moving targets. In low frequency synthetic aperture radar (SAR) system, it is necessary to consider not only kinds of errors that will reduce the coherence of image pairs, but also the unsuppressed radio-frequency interference (RFI) left from the real-time imaging. This paper first analyzes the characteristic of each error in low frequency dual-channel SAR, comparing to those in the high frequency band system, and then analyzes the principle and characteristic of RFI on the interferometric image. A method to improve the performance of along-track interferometric image in low frequency SAR has been proposed further. This method can compensate the difference of receiver frequency, the difference of beam pattern, interferometric error and coregistration error, and use median filters in the azimuth-time range- frequency domain interferometric image to suppress the residual RFI with narrow bandwidth, varying with slow time and radiation angle. The first domestic real data with dual-channel low frequency SAR system has tested the effectiveness and feasibility of this method. It has shown that this method can be operated easily and efficiently with low computation, which is suitable for the real time processing of ATI.