Stability condition and quality evaluation formula of layerlike backfilling roof, Q≥C, where Q denotes is quality index depending on allowable compressive or tensile strength and integrity of backfilling, and C is the technical index depending on mining method and backfilling technology, were inferred according to simply supported beam theorem. Technical treatment measures for instable backfilling roof, including optimum of appropriate filling materials and dosage for excellent flow property and reduction of backfill cost. It is proved that slope equation of backfill slurry in a stope to be filled is y=hexp[-x2/(2σ)2)], where h is height of cone and σ2 is mean square, and that optimum drainage point of backfill slurry can be determined by the equation and sizes of stope. Case study indicates that the results can give a theoretical support for quality evaluation and control of layerlike backfilling.