Influence of steel slag on the percolation structure of cement paste was studied. It is showed that the total porosity of cement paste with steel slag is smaller than that of the control specimens and the specimens with blast furnace slag or fly ash. At the same time, the late properties (about 28 d to 180 d) of cement-based material with 30% steel slag mass addition are better than that of cement-based material with blast furnace slag or fly ash.