Abstract: study on reservoir microcosmic features on chang2 oil group in Xiasiwan oilfield through the microslide, scanningelectron microscopy and mercury-injection method. The reservoir microcosmic features include petrologic features ,diagenesis , pore types, pore throat characteristics ,and so on. Then analyse their main affecting factors . The findings show that the rock component is lower degree of ripeness.The diagenesis mainly are compaction , cementation , clay mineral translation and denudation. Reservoir physical property is affected lightly by the weaker diagenesis. Pore types include residual intergranular pore, katatectic intergranularpore, katatectic intraparticle pore, and so on. The residual intergranular pore is the main pore type in research region;The pore throat is dispersal and its degree of sorting is poor,but its radius is slight thickness. So the reservoir ability is poorer and the oil displacement efficiency is lower.