The particle size distribution of tailing can he considered as a gray system. On conditions of certain water-cement ratio in this system,the compressive strength of ce-mented tailing filling body with a different particle seze distribution in individual curingage is determined,the difference in the contribution of varied particle size to strength in in-dividual curing age is expressed quantitatively with correlativity analysis method of thegray system theory,and an instructive principle of optimaI tailing output obtained in thepractical production is provided