Abstract: The authors studied petrologic characteristics of main rocks by such means as profile measurement of Permian Maihanhada Formation in Yagan area of Ejin Banner, thin section analysis, fossil identification and X-diffraction as well as trace element, clay mineral and heavy mineral analysis. The sedimentary environment of Maihanhada Formation was studied on the basis of lithologic characteristics, palaeophytic fossil, content and ratios of trace elements, and geochemical parameters of gas chromatography on saturated hydrocarbon. It is concluded that the environment of Permian Maihanhada Formation in Yagan area was an offshore to epeiric sea environment characterized by salt water and reduction.