Abstract: A significant breakthrough has been gained in petroleum exploration of Yingxi carbonate reservoir of the lower Ganchaigou formation in Yingxi area of Qaidam basin recently. Based on the core observation, experimental analysis and logging data, the forming mechanism of Yingxi carbonate reservoir and its effects during oil and gas accumulation are researched in this paper. The research indicates that the reservoir was formed in a deep-water sedimentary environment, and the sediment is a set of fine-grained carbonates with some features of diamictite. The reservoir spaces are dominated by dolomite intercrystalline pores, the fracture systems are very developed in the reservoir. The complicated fracture systems are made up of various scales of fractures and play important roles in hydrocarbon accumulation and migration. During the deposition of the upper Ganchaigou formation, the source rocks in the upper member of the lower Ganchaigou formation entered the threshold of oil generation and continuously generated oil and gas. During the late deposition period of Shizigou formation, Himalayan movement resulted in the folding inversion and the Yingxiongling structure gradually formed. The formation process of Yingxiongling structure is not only the formation process of the fracture systems in Yingxi carbonate reservoir, but also is the process of hydrocarbon redistribution in the fracture systems, during which a lot of separate petroleum systems formed