Abstract: The depositional environment and controlling factors for the development of source rock in Langgu sag is studied based on rock pyrolysis and through analysis of organic carbon in more than 1 600 source rock samples, saturated and aromatic hydrocarbon of 65 samples using Gas Chromatograph-Mass Spectrometry(GC/MS), and microelements in 42 samples, and all these samples are selected from the third(Sha-3) and fourth(Sha-4) member of Shahejie Formation in Langgu sag. The results indicate that the ancient climate condition and nutrient elements have an obvious control effect on the development of source rock in Langgu sag. During the sedimentary period of source rock in Sha-3 member, the climate is moist and water of the lake basin is relatively deeper; there is a reducing environment as indicated by the lower Pr/Ph ratio and high V/(V+Ni) ratio. In this period, the water is rich in the nutrients like phosphorus(P), creating a high primary productivity; the algae(dinoflagellates) development is reflected by a high 4-methyl steranes/Sigma C₂₉ steranes ratio. Moreover, as indicated by the development of advanced plants within river basin due to moist climate and high content of aromatic compounds such as retene, cadalene, perylene, pyrene and etc., the amount of terrestrial organic matter is increased and thus results in a high total organic carbon(TOC) content. During the sedimentary period of Sha-4 member, the climate is dry; as reflected by the high gammacerane content as well as high Sr/Ba and B/Ga ratios, the salinity of water is higher leading to salinity stratification. Meanwhile, it is demonstrated by the low Pr/Ph ratio, high V/(V+Ni) ratio and abundant thiophene compounds that the water has an oxygen-deficient reducing environment. However, advanced plants are not developed due to drought climate. Further, there exists limited amount of terrestrial organic matter as demonstrated by the low content of aromatic compounds including retene, cadalene, perylene, pyrene and etc., and quatic organism is dominant in the biological source composition; the nutritive elements(P) is deficient in the water, leading to a low level of primary productivity and also a low TOC content.