Close packing of the fine particles is one of the core technologies of preparation of reactive powder concrete. This paper introduces the concept of soil liquid limit in close packing evaluation. Theoretically, the closer of particles pack, the lower is the water demand. The mixture with a lower water demand is expected to have a lower liquid limit. Mixtures were obtained by measuring the cone penetration at different moisture content. By means of numerical fitting and linear interpolation, the liquid limits of the mixtures were obtained，where the software of Matlab was used. The close packing condition of the powders particles could be predicted according to the liquid limits. Strength test confirmed that application of liquid limit in mixing proportion design of reactive powder concrete is feasible. So, this may be a new way for the preparation of reactive powder concrete.