This paper discusses the particle composition and distribution in cement with large volume of fly ash and their influences on the mechanical property of the cement. Through changing the grinding time and the content of fly ash adulterated into the cement, different samples of fly ash cement are obtained. The relation between the particle distribution and the mechanical property of the cement is analyzed by using the grey correlation analysis method, and the mechanical property of the cement could then be improved with the optimization of the particle distribution. The results show that for the same kind of cement, with different grinding time, the particle zones that dominate the strength of the cement varied; for cement of different compositions, with the same grinding time, the effective particle zones that dominate the mechanical property of the cement also much varied.