The saline lake is one of the most favorable environments for developing hydrocarbon source rocks. In this paper, a sample core from the Qinghai Lake was studied. Based on the relationship of the organic matter content and clay mineral content to the mineral surface area, the authors used the mineral component (or mineralogical phase) to analyze the preservation of organic matter in sediments. Organic matters from abundant terrigenous plants around the lake area composed mainly of microbes and algaes are very rich in the lake. The mineralogical phase indicates that clay minerals are up to 32.4% in sediments at the bottom of the Qinghai Lake, with illite being the main component part. Density fractionation reveals that organic matter content is closely relevant to clay mineral content and mineral surface area in the salified Lake, suggesting that clay mineral adsorption is the major mechanism in the preservation of organic matter in sediments of the Qinghai Lake.