Persistent Scatter (PS) InSAR is an extension to the conventional InSAR techniques. It offers a practical way to reduce the temporal and geometrical decorrelation, and atmospheric artifacts in conventional D-InSAR processing method, therefore can be successfully applied in long-time subtle surface deformation monitoring with multiple SAR images. Surface subsidence mapping due to underground coal mining is one of the application cases in this field. This paper firstly overviews the limitation of conventional D-InSAR technique and the background of PS technique, and then addresses the data processing of PS technique. Several PS related data processors are discussed with aspects of PS pixel identification, algorithm and applicable areas. Undergoing research on monitoring land subsidence in Huainan coal mining areas with PS-InSAR technique is presented as an application example in the end of the paper.