Abstract: The Hg isotopic ratios of coal, dustfall and topsoil from coal fire area No.9 in Wuda coalfield were determined by multiple-collector inductively coupled plasma-mass spectrometry(MC-ICPMS)to explore the possible coal seam source of surface Hg in coal fire areas.The findings were that the δ²⁰²Hg of coal, dustfall and topsoil were -1.98 ‰, -1.30 ‰ and -1.26 ‰, respectively, which showed a significant mass-dependent fractionation(MDF)characteristics.And there were slightly negative anomaly mass-independent fractionation(MIF)values of surface soil, such as dustfall(Δ¹⁹⁹Hg、Δ²⁰¹Hg: -0.13 ‰、-0.11 ‰)and topsoil(Δ¹⁹⁹Hg、Δ²⁰¹Hg: -0.11 ‰、-0.10 ‰).A comparative analysis of the characteristics of Hg isotopic showed that the values of surface soil(δ²⁰⁰Hg、δ²⁰²Hg、Δ²⁰⁰Hg)were all between the No.9 coal seam and the No.10 seam, and closer to the former, which indicated that the Hg source of surface soil in coalfire area No.9 was coal seam No.9 rather than No.10.The δ²⁰²Hg of dustfall was more negative than that of coal seam No.9, which was caused not only by the kinetic fractionation effect of burning and heating process but also by the geologic chromatography effect of migration process in crack and hold.Surface sample Hg isotopes characterizations can be used to distinguish coal seam Hg and then identify the burning coal seam.