Carbonate in lake sediments has an indicative significance for climate and environment. In this paper, the carbonate contents were semi-quantitatively analyzed by meaning of chemical analysis(gasometric method) and X-ray diffraction(XRD method), which were from the sediments of the core KS-2006 of Lake Kusai in Hoh Xil region, Qinghai-Tibetan Plateau. The results showed that there were at least nine kinds of minerals in the core KS-2006, and the measurement error of XRD method(± 5%) was higher than that of gasometric method(± 0.8%). However, the XRD method obtained the average value(18.9%) and variation range(7%-39%) of the total carbonate contents from the sediments of the core KS-2006, which was basically identical with the average value(19.4%) and variation range(5.0%-30.7%) comparing with both of the result. Meanwhile, it showed a positive correlation between the XRD method and gasometric method, and fluctuation tendency with the depth was uniform. This indicated that the XRD method was a reliable method which can be well used to semi-quantitatively analyze the kinds of carbonate minerals and determine their content in lake sediments.