In order to understand the hydrogen isotopic composition of nalkanes in sediments from low latitude freshwater lake and the relationships among hydrogen isotopic composition of sedimentary nalkanes and biological sources as well as ecological environment, nalkanes and their hydrogen isotopes in the systematically sampled sediments from the Fuxian Lake were analyzed using GCMS and GCTCIRMS methods. The δD values of nalkanes in sediments from the lake range from -2193‰ to -1425‰ with average δD values of -2081‰ to -1545‰. According to the δD values of oddnumbered nalkanes, the samples can be obviously divided into two types. The oddnumbered nalkanes in type I samples have heavier hydrogen isotopic composition than those in type II samples. This isotopic difference results from their different biological sources. The results indicate that C17 and C21 to C25 nalkanes were derived from submerged plants in the lake, C27 and C29 nalkanes mainly from woody plants in the surrounding area and C31 and C33 nalkanes principally from the mixture of the aquatic and terrestrial herbaceous plants. The comparison study shows that the ecological environment of lake area is an important factor in controlling hydrogen isotopic composition of lake sedimentary nalkanes. When studying the ancient hydrological characteristics using sedimentary nalkane hydrogen isotopes, the influence of ancient ecological environment should be considered. Only through combination of sedimentary nalkane ACL and Qw values with nalkane hydrogen isotopic composition can we accurately explain the hydrogen isotopic composition and difference of nalkanes in sedimentary organic matter.