The parameters on pore structure of Portland cement pastes blended respectively with 0, 10, 20, 30 and 40% perlite admixture at 3，28，60 curing day were determined by Mercury Intrusion Porosimetre and presented in the paper to investigate affection on performance of cement-based material due to mix the admixture. The research results indicated that since the second hydration reaction had gone on with curing time, perlite admixture could diminish porosity, decrease pore diameter and reduce pore surface area in cement paste. Pores were gradually evolved from original small pores to later smaller pores, moreover fully filled with hydration products and disappeared during hydration reaction. So that the total pore volume in the paste was descended, and the proportion of harmless pores (gel pores and micropores) to whole pores was increased but that of harmful pores (macropores) subtracted. It is concluded that perlite admixture should help to increase the mechanical strength and durability of cement-based materials.