Sediments in Gannan Gahai lake located in the northeast of the Tibetan plateau were systematically sampled. n-Alkanes and their hydrogen isotope in these sediments were analyzed by GC-MS and GC-TC-IRMS. Compositions and origin of n-alkanes and their hydrogen isotope in the samples were studied. The distributions of n-alkanes in the samples showed that they were derived from aquatic and terrestrial plants. The mean δD values of n-alkanes in the sediments range -221.9 to～-190.5‰. The studied samples were obviously divided into two types on the basis of δD values of C21-C33 odd carbon number s. The n-alkane δD values for type 1 samples indicated that the n-alkanes come from aquatic plants in Gannan Gahai lake, while those for type 2 samples showed that they were derived from terrestrial herbaceous plants. It was considered that the medium-chain length n-alkanes with high content, low δD values and low CPI values were derived from bacteria by which sedimentary terrestrial herbaceous plants were transformed. The studied results further confirmed that n-alkanes in sediments record the hydrogen isotopic composition of source water used by organisms. Therefore, δD values of sedimentary n-alkanes can be used as geochemical indicators of paleoclimate and organic matter source.