Abstract: The reservoirs of Jurassic Lianggaoshan formation and Sha-1 member of Shaximiao formation in Sichuan basin are typical extra-low porosity and extra-low permeability reservoirs with strong heterogeneity and great difficulties to predict sweet spots. To predict the favorable areas of sweet spot, the paper studies the reservoir characteristics and its forming mechanism based on the analysis of core, thin section, SEM, X-ray diffraction and inclusion. The study results show that the Jurassic tight sandstone reservoirs are the products of the dissolution of facies-controlled sandbodies during the middle diagenetic period in the Sichuan basin and the structural fractures formed in the middle and late periods can improve the reservoir capability. The sweet spots in the reservoirs are controlled by sedimentary sandbody, diagenetic dissolution and structural fractures, and mainly distributed in the areas where microfacies such as beach bar, distributary channel and river mouth bar, hydrocarbon charging phases and fractures superimpose with each other. The sweet spots of Lianggaoshan formation are mainly found in the areas of Gongshanmiao, Longgang-Yingshan, Lianchi-Chongxi etc.; and the sweet spots of Sha-1 member are mainly distributed in the areas of Gongshanmiao, Wellblock Longgang-9, Shuijiacao and Dacheng-Guang’an etc