When the multi-channel SAR system is used for moving target indication, the imbalance in amplitude and phase among channels severely affects the performance of moving target detection and parameter estimation. For multi-channel low frequency SAR/GMTI system, a multi-channel equalization method based on subaperture image was proposed. The method makes use of multi-channel subaperutre images with the same view-angle, and estimates the amplitude and phase errors related to this view-angle at the same time. It can estimates the amplitude and phase errors accurately and adapts to the errors changing with the view-angle. The experiment based on vehicle-borne low frequency multi-channel SAR/GMTI real data demonstrates that this method can effectively compensate for the amplitude and phase errors among different channels and improve the performance of moving target detection.