Two kinds of natural hydraulic fracturing were found in laminated argillaceous dolomite and homogeneous argillaceous dolomite of the Upper Xiaganchaigou Formation in the Shizigou Structure in the southwestern Qaidam Basin (SW Qaidam Basin). To explore the geometric characteristics of networks of natural hydraulic fracturing, the temperature-salinity conditions when hydraulic fracturing occured, the interaction between fluid in fractures and surrounding rocks, and controlling factors of natural hydraulic fracturing under the background of multiple overpressure factors, the two kinds of multilevel fracture networks and inclusions in veins were described at the core scale and thin section scale under single polarized light, orthogonal light and cathodoluminescence. Types, distribution, and contents of minerals in veins and surrounding rocks were further characterized by TESCAN integrated mineral analyzer (TIMA). In addition, the homogenization temperature and salinity of aqueous inclusions in veins were tested. Results show that natural hydraulic fracturing in laminated argillaceous dolomite and homogeneous argillaceous dolomite has similarities and differences. Regarding similarity, both fracture networks consist of three-level veins, including the main vein, the first-level hydraulic veins, and the second-level hydraulic veins, showing orthogonal nets in cores. In addition, anhydrite is the main filling mineral in veins. The differences are as follows. Firstly, the first-level hydraulic veins develop along the lamina directions that intersect the main vein with an angle in laminated argillaceous dolomite, while the first-level hydraulic veins are perpendicular to the main vein in homogeneous argillaceous dolomite. The thicker vein inhibits the development of thinner veins which are nearly parallel to the thicker one. Moreover, thinner first-level and second-level hydraulic veins in homogeneous argillaceous dolomite are mostly filled by calcite and celestite. Secondly, only low-mature heavy oil inclusions develop in the main vein in laminated argillaceous dolomite, while in homogeneous argillaceous dolomite, only aqueous inclusions develop in the main vein, and heavy oil traces exist in intergranular cleavage and secondary fissures. The average homogenization temperature of aqueous inclusions (215℃) is greater than the paleogeothermal range (35–150℃) controlled by the burial depth of the sample. Considering multiple overpressure backgrounds, the tectonic evolution history, thermal history, burial history, and hydrocarbon accumulation history, we propose that natural hydraulic fracturing in the laminated argillaceous dolomite may be attributed to the superposition of tectonic compression, gypsum-anhydrite transformation, and hydrocarbon generation. Hydraulic fracturing in homogeneous argillaceous dolomite is attributed to overpressure caused by upwelling of deep thermal fluid. During the reaction between hydrothermal solution and surrounding dolomite, celestite in thin veins is beneficial to enrichment by extracting Sr2+ from surrounding dolomite. Formation process and geometrical patterns of two kinds of hydraulic fracturing have enlightening significance for enrichment of celestite deposits and the current artificial hydraulic fracturing of shale oil reservoirs in the upper Xiaganchaigou Formation in the SW Qaidam Basin.