The ground-based SAR, as a new type of ground remote sensing technology, is widely used in the field of microdeformation monitoring because of its high precision, all-weather, flexible and real-time continuous observation. Based on the deep research on the key technical problems of micro-deformation monitoring of ground-based SAR, combined with the characteristics of foundation pit monitoring, the method of weighted median filter denoising was used to improve the signal-to-noise ratio of interferogram and weaken the noise phase difference. The method of atmospheric correction based on the PSC network was proposed to reduce the impact of meteorological disturbances and weaken the atmospheric phase difference. The improved methods were applied to the foundation pit monitoring experiment. The experimental results show that the weighted median filter and PSC network weather correction effectively weaken the phase change caused by noise and atmospheric, and achieve monitoring accruacy of submillimeter. In order to verify the accuracy of ground-based SAR monitoring, the synchronous observation is carried out using high-precision total station, the monitoring results are consistent with the results of ground-based SAR, which verifies the reliability and feasibility of ground-based SAR technique in monitoring the microdeformation of pits.