Abstract: Reservoir of the Lower Cretaceous Shahezi Formation in Xujiaweizi Fault Depression in the northern Songliao Basin is characterized by close provenance, rapid facies change, strong heterogeneity and superimposed source rock and reservoir, which has geological conditions for the accumulation of tight gas reservoir. The study results show that reservoir of Shahezi Formation is tight with low textural maturity. The lower limit of pore throat for fluid flow is 20 nm and the upper limit of pore throat is 0.4 μm of the tight reservoir. NMR and high pressure mercury injection experiments on core samples of Shahezi Formation indicate that the reservoir physical properties were greatly affected by sediment grain size. Firstly, the reservoir types are classified according to different lithologies such as tight sandstone and glutenite. Then the sweet spot evaluation method of “subdivision after classification” is innovatively researched for tight reservoirs in fault basin based on the comprehensive factors such as porosity, reservoir thickness, and shale content affecting on single well production. As a result, 31 sweet spot areas are divided in the entire area and totally 230 sweet spot bodies are identified. Among them, Anda area in the northern Xujiaweizi Fault Depression is an optimal sweet spot area, with sweet spot bodies of the underwater distributary channel, sheet sandstone and channel mouth bar microfacies of delta front facies are well developed, which provides guidance for the exploration deployment in this area.