The effects of mineral admixtures ultra fine pulverized fly ash, pulverized slag and silica fume on the denseness of fresh cement paste were quantitatively studied with the index of relative denseness. The relationship between the fluidity of fresh cement paste containing mineral admixtures and relative denseness, as well as the influence of relative denseness on compressive strength of mortar are analyzed to expect to further expound the physical filling effect of mineral admixtures.