Fly ash powder,which was grinded to different particle size distribution,was mixed in a series of proportions with Portland cement.The particle size distribution with the theory densest packing was obtained according to Dinger-Funk equation and the practical particle size distributions of fly ash cements were calculated according to the tested results of the cement and fly ash powder by LS-230 particle size distribution instrument.The relationships between the particle size distribution with the theory densest packing and practical particle size distributions of fly ash cements were studied by the grey connection analyses method.The water consumption of standard consistence of fly ash cement and mortar compressive strength were tested to provide the(theory) analyses.The results indicate that fly ash cement would have better properties when the(value) of grey connection degree between the practical particle size distribution of fly ash cement(and particle) size distribution with the theory densest packing is higher.