Abstract: The reservoirs from Chang-8 formation in BanqiaoHeshui area, Ordos basin were characterized by poor reservoir property and complicated oil-water relations, and there existed great difficulty in exploration. By use of the techniques of physical properties, casting thin slices, scanning electron microscopy and high-pressure mercury,in combination with the theoretical knowledge of petrology and sedimentology, the research on reservoir characteristics of Chang-8 reservoir and its main controlling factors were carried out. Results indicated the rocks of Chang-8 reservoir were mainly fine lithic-arkoses. The residual intergranular pores and solution pore developed well.The complex pore structure led to strong microheterogeneity. The study area mainly developed the delta-front facies, and the physical properties of reservoir are determined by the facies. Underwater distributary channel sand body were the most favorable reservoir facies. Through the study of diagenesis, it was considered the study area had undergone strong compaction, which greatly reduced the primary pores of the reservoir. Cementation had both destructive and constructive effects on the physical properties of the reservoir. The results indicated there were many dissolution pores formed because of the dissolution, which played a key role in improving the physical properties of the reservoirs.