Abstract: In order to study the stability of “filling body-coal pillar” composite structure in roadway backfilling mining, the bearing characteristics of composite structure are analyzed. The expressions of potential energy function of backfill bearing part and coal pillar bearing part of composite structure are established. Based on the catastrophe theories, the critical conditions for swallow tail mutation of potential energy are analyzed and the instability discrimination formula is given taking the width of plastic zone as the main index. The effects of mining parameters such as mining roadway width, coal seam buried depth and the number of mining phases on the stability of composite structure are studied. Using the numerical calculation method, combined with the engineering case of Wangtaipu Coal Mine, the bearing parameters such as the vertical stress distribution characteristics and the width of plastic zone of the composite structure are analyzed. The accuracy of the instability discrimination formula of the composite structure is verified.