Abstract: The Ⅳ oil member of the upper section of the lower Ganchaigou formation in the Yuehui 101 area of the southwestern Qaidam basin belongs to tight lacustrine carbonate reservoirs, which lacks of quantitative characterization basis for its brittleness evaluation. The key technology for tight oil reservoir brittleness evaluation is discussed based on the tight reservoir brittleness prediction. At first, based on the whole rock mineral analysis by core X-ray diffraction, the brittleness index of rock sample is calculated qualitatively by using mineral content. Based on high-temperature high-pressure triaxial mechanical tests and acoustic triaxial experiments for rocks, the brittleness index of the sample is calculated quantitatively and furthermore, the transforming relations between the static and dynamic Young’s modulus and between the P-velocity and S-velocity are determined. Secondly, the simultaneous inversion technology of pre-stack elastic parameters is used, the P-impedance, S-impedance and density data are obtained. Then Young’s modulus and Poisson’s ratio are calculated, and the dynamic and static Young’s modulus relations are used to convert them into the static Young’s modulus, so as to complete the calculation of static brittleness index. Finally, the distributions of brittleness and lithology in the target zone are analyzed to identify the key areas for tight oil exploration, and the effectiveness of the method has been verified by subsequent well drilling