Abstract: In order to rebuild the sedimentary environmental conditions of Shanxi Formation in Chaohua coal mine,Henan Province,the clay mineralogy and geochemistry have been analyzed with XRD and ICP.the results show that the contents of trace elements and clay minerals are obviously different in the mudstones above and under No.2-1 coal seam of Shanxi Formation.The contents of B、Sr/Ba、P、CaO、MgO、V、Li、Ni、Zn are higher in the floor mudstones,but rapidly decrease in the mudstones above coal seam.TiO₂、Cu and Co have the opposite change trends to the elements above stated.The contents of Illite and I/M mixedlayer clay mineral are higher in the floor mudstones,but Kaolinite is higher in the mudstones above coal seam.The results suggest that the influence of marine water is obvious on the formation of floor mudstones,but rapidly weak after the formation of coal seam.