Abstract: In order to study the stability of filling body in the process of filling and replacement of interface coal pillar, based on the geological conditions of a mine in Yushen Mining Area of Shaanxi Province, the calculation models of filling body load during tunneling, primary mining and the secondary mining were established respectively, and the critical width value satisfying the stability of filling body was obtained. The filling material ratio scheme meeting the requirements of filling replacement strength was given through laboratory tests, and the stress and elastic-plastic zone distribution characteristics of filling body were analyzed by numerical simulation. The research shows that under the conditions of different filling body widths of 8 m, 12 m, 16 m and 20 m, the stress concentration factors of the filling body are 1.79, 1.61, 1.55 and 1.54 respectively during the tunneling period, and the development range of the plastic zone of the filling body is 2 m, and the main failure form is shear failure; during the first mining period, the stress concentration factors of the filling body are 3.66, 3.26, 3.04 and 2.93 respectively, and the range of the elastic zone in the middle of the filling body is 0 m, 3 m, 5 m and 10 m respectively; during the secondary mining period, the stress concentration factors of the filling body are 4.78, 4.19, 3.91 and 3.74 respectively, and the elastic zones in the middle of the filling body are 0 m, 2 m, 4 m and 8 m respectively. With the increase of the width of the filling body, the decrease rate of the stress concentration coefficient of the filling body tends to be gentle, and the stress distribution curve gradually presents the shape of “double peak and single-valley”. Combined with theoretical analysis, it is considered that the filling body can maintain good stability when the width of the filling body is not less than 16.7 m, and the research results provide a theoretical basis for the filling and replacement of interface coal pillar under similar geological conditions.