The distribution characteristics of normal alkane in the lake sediments can be used to indicate well the organic sources and deposition environments. In this paper, some surface sediments on lake bottom in Koh Xil area, high altitude cold area in the northern part of Qinghai—Xizang(Tibet) Plateau, were collected. After analyzing the n alkane in the sediments, the n alkane distribution characteristics and the environmental significances are abtained. It is shown that the distribution of n alkane can be controlled by terrestrial and aquatic plants and lake salinity. n alkane C31 predominance from terrestrial plants has been existed in almost all lakes in this area. Mid chain length n alkanes (C23~C25) have been shown in the lake sediments with aquatic plants developing and have a high carbon number n alkane (C27, C29, C31) contribution. n alkane from aquatic plants of Potamogeton malaianus has an predominance C23 peak and C31, C29, C27 peaks. In the salt and brackish water lakes, high Ph exists. That different mid chain length n alkanes and no even carbon n alkanes in the high salt lakes is the reason of the different component and distribution of n alkanes in the lake sediments. At the same time, C27 and C29 predominance peaks do not always come from terrestrial woody plants, but with the same characteristic from aquatic plants.