14 samples of No. 4 coal seam are taken from the Chuancaogedan Coal Mine,Jungar coalfield,Inner Mongolia. Combined with coal plant type and sedimentology characteristics,the petrographic properties and coal facies type of the coal were analyzed by use of coal microscopic method.The results indicate that the maceral of the No. 4 coal seam is enrichment in vitrinite. In the whole evolution process of the swamp,the No. 4 coal was deposited dominantly in moist forest peat marsh,as well asin open moor and shallow water forest swamp facies occasionally. The evolution of the swamp can be divided into two stages. The extent of the overlying water in the No. 4 coal seam from bottom to top shows a strong-weak-strong change. There are two types of swamp hydrodynamic conditions in the No. 4 coal,the retention swamps and running water swamps periodic appear alternately.