Abstract: As an important biological element, nitrogen is causally linked with organic matter accumulation, but a systematic and regular understanding has not been developed. This paper discusses this issue by taking the widely developed Permian-Paleogene terrestrial (lacustrine) hydrocarbon source rocks in China as an example. The results show that the terrestrial source rocks in China can be classified into three groups according to the nitrogen isotope (δ¹⁵N) compositions and combined with the salinity and evaporative alkali mineral characteristics: the circum-neutral group 1 (average δ¹⁵N=4.0‰±1.5‰), the circum-neutral group 2 (average δ¹⁵N=7.1‰±1.6‰), and the alkaline group (average δ¹⁵N=18.4‰±3.3‰). In the circum-neutral group with δ¹⁵N < 10‰, the δ¹⁵N of the source rocks is positively correlated with organic matter abundance, type, hydrocarbon generating capacity and shale oil potential due to the fact that higher δ¹⁵N characterizes changes in the composition of the hydrocarbon generating bio-precursors. In the alkaline group with δ¹⁵N>10‰, the organic matter types are good and shale oil potentials are higher, but the response relationship between δ¹⁵N of source rocks and organic matter accumulation is not as good as that of the circum-neutral group, reflecting that the organic matter accumulation in alkaline group is influenced by other comprehensive factors other than δ¹⁵N. Accordingly, the organic matter accumulation models of three types of lacustrine source rocks (< 5‰, 5‰-10‰, and >10‰) classified on the basis of δ¹⁵N were established. The δ¹⁵N has the potential to trace organic matter accumulation and quality of source rocks. For example, low δ¹⁵N type (δ¹⁵N < 5‰) is of poor quality and medium-high δ¹⁵N type (δ¹⁵N>5‰) is of good qualityin lacustrine source rocks. This paper enriches the biogeochemical and hydrocarbon source rock geochemical studies of nitrogen by exploring organic matter accumulation in source rocks from the new perspective of nitrogen isotope composition and nitrogen cycling.