Sludge gasification slag（SGS） was designed to prepare backfill concrete which was used to completely replace the coarse and fine aggregate in concrete， which was applied in laboratory and practical engineering simultaneously. The results show that the good water absorption of SGS can play the role of internal curing in concrete as aggregate， and improve the interface transition zone of concrete， which indicates the feasibility of the application in backfilling concrete. Response surface method was used in the concrete proportioning design and the optimal mix ratio is obtained in this experiment as follows： sand rate is 60%， the proportion of 5-10 mm particle size in coarse aggregate is 60%， and the pre-wet water consumption is 90%.