Abstract: In the light of perfect gas law,the manufactured apparatus can be used to determine vari-ous sorts of porosity of an unconsolidated mass of materials directly, and it is suitable to these materials with high hydroscopicity, especially for those dissolving easily in water and complicated to determine specific gravity. This apparatus is accurate, simple and convenient. Determined results on porosity of an unconsolidated mass of materials in different state of placement,different content of impurity and different composition in sizes,are of value for reference.