The sedimentary environment of middle Permian Zhesi Formation in Suolun area was studied on the basis of lithology and sedimentary structure, in combination with the content and ratios of trace elements as well as geochemical parameters of saturated hydrocarbon, then to discuss relative change of sea-level and the evidence for evaluation of oil/gas geologic conditions of Carboniferous-Permian was provided. It indicates that Zhesi Formation mainly belongs to marine sedimentary environment under the condition of warm-humid climate and semi-salt water; the range of palaeosalnity is 18.55‰~28.72‰, The paleosalinity and the change of water depth are showed by the trace elements and their ratios, which are impacted by the change of sea-level. Palaeosalinity and relative change of sea- level has a good correlation with sedimentary facies evolution. Using the quantitative calculation Palaeosalinity and the values which reflect the paleosalinity and the water depth of Sr/ Ba, B/Ga and Rb/ K ,the curve of relative change of sea-level of Zhesi Formation was established. The Zhesi Formation had undergone two transgression-regression cycles and the transgressions take place in the bottom and middle part of Zhesi Formation. According to sedimentary facies analysis and the geochemical index, showed that main body of Zhesi Formation was formed in an neritic shelf environment characterized by oxygen deficient and reductive conditions ,which is conducive to the preservation of organic matter and development of hydrocarbon source rock.