Abstract: Taking 845 working face of Muchengjian Coal Mine as prototype, this paper studied the law of stress and displacement of roof and floor in the process of backfilling in steep coal seam by using polyethylene plastic foam board as backfill and taking the method of backfilling while mining. It indicates that the style of backfilling can control the crack propagation and stress concentration of the roof and floor to avoid the caving of the large roof and the heaving of the floor.