By studying the trace elements of the Permian dark mudstones in Ejinaqi and its surrounding Areas，it indicates that it was semi-salt water sedimentary environment during the Permian in this area. Vertically, the water salinity is gradually reduced, which is synchronous with the extinctive process of the rift basin. Horizontally, the eastern（Western Yagan areas）salinity is obviously higher than the western (Beishan areas), which is related with sedimentary paleogeography-with a deeper sea water in the eastern and is consistent with the distribution characteristics of the paleontology. Combing the analysis of V/V+Ni with Ceanom about mudstones indicates that it is reductive environment during the Permian period, which is helpful to the saving of the organic matters. The environment reductibility in the north-eastern area is higher than the south-western area, which controls the distribution of the organic matters. Studying the environmental characteristic has some guiding significance to look for potential favorable hydrocarbon source rocks for us. Combing the distributive pattern of the rare earth elements from dark mudstones with field geological survey indicates its province is from the upper crust and its parent rocks are the mixing of claystones and granite rocks in the studied area.