Unconventional tight sandstone reservoir resulting from deepwater gravity flow, as a new hotspot for hydrocarbon exploration and development, has attracted much attention.The deepwater depositional environment is characterized by complex hydrodynamics, resulting in large variation in type and content of interstitials, and strong heterogeneity of reservoirs under microscopic observation, thus challenging petroleum E & P.In this study, an integration of casting thin section and SEM observation, Quantitative Evaluation of Materials by Scanning Electron Microscopy (QEMSCAN), electron microprobe and nano CT analysis, is applied to finely characterize the microscopic features of various interstitial matter in the deepwater tight sandstone of the 6th member of Yanchang Formation (Chang 6 Member) in Huaqing area, Ordos Basin, and discuss the effects of interstitials on reservoir pore structure and physical properties.The results show that the matrix is not completely tight, which could, under diagenetic modification, generate a complex secondary pore network consisting of intercrystalline and dissolved pores with a pore size ranging between 20 nm and 1 000 nm.With a matrix content of less than or equal to 7%, the matrix contains well-developed secondary pores, which has a positive impact on reservoir quality; with a matrix content of greater than 7%, the secondary pore development is undermined, exacerbating reservoir compaction.The intercrystalline pores in clay mineral cements, however, could alleviate the reduction of porosity to some extent; on the other hand, the morphology, occurrence of different clay minerals, and their effect on reservoir sensitivity, function to increase the complexity of clay mineral-permeability relationship.In areas with high content of illite, I/S mixed layer and thick chlorite, the reservoirs are commonly poor in physical properties; while high-quality reservoirs are most seen in areas of well-developed kaolinite.Carbonate and siliceous cements are key in undermining the physical properties of deepwater tight sandstone reservoirs.In all, the area with a matrix content of 7% or less and relatively well-developed kaolinite cement is a focus for the exploration and development of tight sandstone reservoirs of deepwater facies.