The sandstone reservoir characteristics of Dainan 1 Formation of Yongan area in Gaoyou sag are analyzed. The results show that the sandstones are mainly feldspathic litharenite with low compositional maturation, fine grain, and medium-bad sorting degree. The reservoirs are mainly of low porosity and low permeability, and supplemented of medium porosity and medium permeability. The research indicates that the sedimentary factor is one of the main controlling factors of the sandstone reservoir quality of Dainan 1 Formation of Yongan area in Gaoyou sag, and the sandstone formed in the sedimentary environment with high hydrodynamic intensity has good reservoir quality with large grain and good sorting. Different kinds of diagenesis have different effects on reservoir quality.