Abstract: The tight oil in Permian Lucaogou formation of Jimsar sag is the important target for terrestrial unconventional oil and gas exploration in China. In order to describe and predict the difference in densification process of terrestrial tight reservoirs, and to define the development model of the sweet spots, the paper takes the tight reservoir of the Permian Lucaogou formation in Junggar basin as an example to analyze the interaction of diagenesis within the closed diagenetic system of the Lucaogou formation, reveals various reservoir densification paths and clarifies the development mechanism of sweet spot based on the data of thin section, SEM, physical property, stable carbon and oxygen isotopes analysis and fluid inclusion homogenization temperature. The research indicates that according to their diagenesis evolution paths,four densification types of the tight reservoirs in Lucaogou formation are summarized such as weak dissolution of carbonate rock, strong compaction of plastic debris, normal compaction and strong calcite cementation, and carbonate cementation + clay mineral cementation and superposition. Three forming mechanisms of sweet spots are classified including primary pore preservation of local overpressure and early chlorite protection, one period of strong dissolution and superposition of two-period dissolution. These three types of sweet spots are more likely formed in the dominant sedimentary microfacies with high terrigenous clastics content such as thick sandy beach bars and distal bars in deltas