Objective: It is generally believed that the tight sandstone reservoir has strong heterogeneity and poor physical properties, but the tight sandstone reservoir in the Jimsar Sag, Junggar Basin, has good oil and gas production. Through the core data photos, it is found that the reservoir fractures of the Jinjinzigou Formation (P2jj) in the study area are developed, most of which are filled with crude oil and calcite. Based on the microscopic thin sections and scanning electron microscope photos, it is found that most samples develop micro-fractures. Through the observation, measurement and calculation of micro-fractures under the microscope, combined with the core and regional tectonic background, the development characteristics, main controlling factors and genetic mechanism of micro-fractures were systematically analyzed, and the formation stages of micro-fractures were discussed. The research results have guiding significance for the genesis of micro-fractures in tight sandstone reservoirs and the evaluation of high-quality reservoirs in the Junggar Basin, and can be used as a reference for oil and gas exploration in tight reservoirs with similar geological conditions.