IBIS-L ground based SAR is able to provide accurate and long-term measurements over relative large areas by combining of stepped frequency continuous wave, synthetic aperture radar and interferometric technique. To measure displacements of an open pit slope in Beizhan iron mine, a novel environmental correction method is presented to perform the atmospheric distortion correction of GB-InSAR. GB-InSAR results show that, the entire working area is mainly on a stable condition, only two remarkable displacement areas with the maximum displacement over −15mm locate in the upper and lower parts of quarry rock face, respectively. Considering the displacement evolutions of selected pixels at different sectors, the quarry rock face should be impossible to produce larger geological disasters.