Normal style="MARGIN: 0cm 0cm 0pt">The Wucaiwan coalfield, which contained the heavy coal seams in the Xishanyao Formation in Jurassic, was located in the western part of the Eastern Junggar Basin, Xinjiang, and the thick coal-seam was successively and steadily distributed with high coal quality, which was the main explore object. so the author apply the theory knowledge and method include of coal geology, coal petrology, coal geochemistry and deposition etc.further approach the Xishanyao Formation thick coal seams's petrology composition and coal facies, and the result indicated: Macerals of the coal seams was dominantly made up of Vitrinite (mainly telinite, detrovitrinite and corpovitrinite) and secondarily Inertinite (fusinite and semifusinite), with little liptinite. Coal facies study showed the coal was mainly formed in the wet forest swamp and secondarily in the dry forest swamp. Few studied samples indicated shorted and periodic the overlying water forest swamp and the open water swamp depositon during the coal-accumulating stages. The analysis of the coal petrology and coalfacies interpreted the characteristic of coalforming environment was the braided channel delta.which also had provided some basis for the analysis of coalforming environment, assessment and the coal quality and the preparability.