Abstract: The paper aimed to ilustrate a rational design on backfill body口s compression ratio( BBCR) in waste backfilling coal mining,which could save the amount of waste backlilling and ensure the safety of dam. Firstly,the authors theoretically analyed on factors that influenced the value of BBCR and each factorDs actual effect of the BBCR. Secondly,a case studied on waste backfilling coal mining in Jining No. 3 Coal Mine under Nanyang Lake Dam to elaborate the BBCR dynamic design according to t he damDs feature and the coal mining specification to define the fortification standard and with the surface subsidence prediction using fully caving method to define the a mount and range of waste backfilling,as instance,the BBCR should be at least 15.8% when the mining face was 340 m away from the dam,and the BBCR levels up as mini ng face goes closer to the dam,the BBCR should reach 91.8% as the mining face was 60 m away from the dam.Finally,a conclusion according to the surface subsidence pr ediction using equivalent mining height model that the rational BBCR design not only ensured the safety of the dam,but also saved flling materials and provides scientific b asis for the layout of the project.