The Triassic low permeability reservoir sandstone of Yanchang Formation in Ordos Basin is composed of fine-grained arkose and feldspathic litharenite. It is considered that the formation of secondary pore through dissolution of laumontite improved the reservoir property of sandstone, and the dissolution of laumontite was closely related to alteration of plagioclase. Combined with regional geological evolution history of Ordos Basin, the authors hold that albitization of sandstone reservoirs in Yanchang Formation of Ordos Basin was related to hydrothermal activity of Yanshanian period. It is suggested that the hydrothermal diagenesis of sandstone was closely related to the formation and distribution of oil reservoirs and therefore deserves attention and research.