Based on analysis of cores, cast thin section, scanning electron microscope, mineral and physical properties, the sandstone reservoir characteristics and its influencing factors of Taiyuan Formation in northeastern Ordos Basin are studied. The lithology of the reservoir in the study area is mainly sublitharenite, with high compositional maturity, middle-high textural maturity and poor properties. It is lowporosity and lowpermeability reservoir. The reservoir space is dominated by secondary pore. The rarely developed diagenetic microfractures made little contribution to improving the reservoir permeability. The reservoir quality is controlled by sedimentary facies and diagenesis. Sedimentological analysis shows that tidal channel is the favorable sedimentary microfacies of reservoir. Reservoir pore evolution is dominated by compaction, cementation and denudation. The decrease of sandstone porosity is mainly caused by compaction. Siliceous cementation and authigenic illite further reduced the porosity and permeability. Carbonate cementation continued to late diagenetic A stage. The cementation in the early stage enhanced the preservation of primary pores, and the cementation in the late stage damaged secondary pore.