Forty-four samples of the No. 6 Coal were taken from the Guanbanwusu Mine, Junger Coalfield, Inner Mongolia, in 2009 in order to study trace elements. Twenty-two trace elements of the samples were analysed by ICP-MASS method. The results show that Li, Se and Ag are significantly enriched in the No. 6 coal. Most trace elements are enriched near the roof and floor. The content ratios of Sr and Ba, V and Ni, V and Zn might indicate that the peat swamp of this area during this period is influenced by sea water or in a sea-land transition environment. The enrichment of Li, Se, Ag shows that it formed in a relatively oxidated environment, and ancient water salinity is slightly high. In harmful elements, only Se is significantly enriched. The contents of the other harmful element are low, and do not pose many hazards to the environment. They can be partially removed by physical coal washing.