Abstract: In Lucaojing area of Ejinaqi,the dark mudstone with a extreme thickness in Jushitan Formation of Middle Permian series is well developed.its TOC content reaches 0.5%,and the parameters of C₂₉ααα-20R/(20S+20R) and C₂₉αββ/(αββ+ααα) Biomarker show that the source rock is mature-high mature,which is beneficial for hydrocarbon generation.In this paper,we analyze the sedimentary environment in order to investigate the extension of sedimentary facies belts benefitting for source rocksbecause the investigation has an important significance to oil and gas exploration about rift basin of Carboniferous-Permian in Ejinaqi and its adjacent area.According to lithologic association,sedimentary characteristics,biomarker characteristics,and regional tectonic evolution,we research the middle Permian series sedimentary environment.Through the analysis about distribution of C₂₇,C₂₈,C₂₉ Sterane and the ratio of the pr to Ph of the isoprenoid,we build the relation between it and sedimentary environment.By doing so,we can discuss the application of the sedimentary environment through biomarker characteristics.