To solve the problem of low coherence in the interference superposition of the coherence map generated by the traditional single main image, this study proposes a weighted superposition method based on the differential interferometric synthetic aperture radar (D-InSAR) with multiple main images. This method uses fewer SAR images to generate interferograms, and relies on the weighted superposition method to avoid the involvement of coherence maps with low coherence in the superposition, so as to achieve high-accuracy and long-time deformation monitoring in a certain area. Firstly, multiple main images are selected to generate multiple interferogram sets. Secondly, the multiple sets of coherence maps are superposed according to the weight. Finally, the average velocity maps of surface deformation in different time periods are obtained. In this study, Sentinel-1A data of 9 scenarios from July 2019 to December 2019 were selected from San Diego City in the United States for experimental verification, and the experimental accuracy was verified by the comparison of the experimental results with groundwater monitoring data. The experimental results show that this method not only reduces the number of images required for the experiment, but also improves the quality of the interferograms involved in the superposition. It produces better monitoring results than the traditional D-InSAR in improving the monitoring accuracy.