Abstract: In order to forecast, explore and cxplmt relative high quality coals,it is necessary to understand the law of sulphur and ash contents and the factor controlline the chanemg law.For this reason the study on the coal qualUy of coal scams No:I₄.IV₄ and V₂,were formed in different accumulationg enviromcnts and is located to Yuxtan coal district, Hcnan, have been taken b> the auther. The rsuit shows that the range of the sulphur content of the coal Seam formed in salt water is>3%,in cxist as straw berry pynite.The sulphur content of the coal Seam formed in salt water is<0.6% and this sulphur mainly exists as crgan sulphur. As content is coals is bound up with coal一accumulation cwiroment and disturbing degree of swamp water.The coal seams formed in the cabonatous shore with clear water and sight disturbance usually contain clow ash content.The coal scams developed In the scawardarea of abandoned delta with the dlsturbing water and detrital supplement frequently contain the relative high ash content; and in the landward area of abandoned delta, the relative low ash content. The ash component in coal reflects the character of swamp water. With increasing the water salinty in swamp, ash component specific value(K=(SiO₂+Al₂0₃)/(Fe₂O₃+Ca0+Mg0+SO₃))gradually dc- creases. The coal seams formed in fresh water swamp, K=10-3.5; in salt water swamp, K<3.5- In same coal seam the change of sulphur content is responsible for the depth of water in swamp. The depth was mainly controlled by the ancient topographical feat ures which were efTected by the thickness of underlying sandstone. Where the underlying sandstone is relative thick, the defferent compact is smaller, generally formed higher landforms, therefor the coal seams formed under the shallow water usully contain lower sulphur. These character is opposite from the places where under lying sandstone thickness is small. The higher landform in swamp catches the deposits carried by wind casyly，then the coal scams contain higer ash content. Whether depositional enviromcnt of coal roof will effect the sulphur content and sulphur type in underlying coal scams is determined by the lasting tirvc of the environment of coal roof. The longer the lasting time, the more marked efTect. Combining the change features of sulphur and ash contents with the study of depositional and coal-acumulating enviroments, it is posible to forecast, explore and exploit the coal with lower sulphur and ash contents in where coal seams is consided containing high sulphur and ash contents.