Through a sampling analysis of trace elements and ＲEE in the section of Middle Permian Zhesi For- mation in Solon area of Inner Mongolia，it is found that the overall sandstone and mudstone samples are charac- terized by LＲEE-enrichment． By analysis of the discriminant index of the sedimentary environment，the tectonic setting of Zhesi Formation is determined to be a continental island arc environment． Meanwhile，according to the sedimentary structure and lithology combination，Zhesi Formation is divided into the neritic-bathyal reten- tion-reduction environment as well as the delta front and prodelta sedimentary systems．