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The reservoirs of the Songliao Basin are composed of typical unstable sandstones, with high percentages of volcanic fragments and feldspar. In the course of sedimentation and burying, a series of physical and chemical reactions took place between minerals and pore water and water-rock reactions and ion exchange caused changes in ion assemblage of pore water. Hydration-hydrolysis, dissolution and the albitization of feldspar made many ions free from their framework and inter into the pore water, and induced the precipitation of a large amount of authigenic minerals such as smectite and chlorite. During the diagenesis of sandstone, diagenetic reactions involved several stages with increasing depth, and so did the precipitation of authigenic minerals and the transformation of minerals. The migration of ions is related with the precipitation, transformation and dissolution of authigenic minerals. Thus, to deepen our study on sandstone diagenesis is an important link for the analysis of ion migration in the evolution of pore water. The origin and evolution of pore water could be tracked in terms of the geochemistry of fluid inclusions in authigenic minerals. And the isotopic composition of the authigenic mineral calcite can provide its genetic information.