Hydrothermal sedimentary structures，textures and complex saline minerals widely distributed in the deep—semideep lacustrine facies “white smoke type” dolomitic exhalative rock in Lower Permian Fengcheng Formation in Urho area, the northwestern margin of Jungger Basin. This article prove that the dense oil reservoir of dolomitic rock in Fengcheng Formation belong to “white smoke type” exhalative rock with special genesis by way of presenting a deep analysis of REE geochemical characteristics based on the study about petrology and mineralogy. In addition, this paper discuss about the characteristic of hydrothermal fluids and sedimentary environment.