The ongoing underground coal fire in Wuda coal field, Inner Mongolia, China started over 50 years ago and continues to pose environmental and biological hazards. To investigate its potential impact on local plantation, a total of 298 Bassia dasyphylla (sandwort) leaf and stem samples were collected at Wuda coal field, and the mercury level was determined by Lumex RA-915M/PYRO-915+ mercury analyzer. The average mercury concentration in the leaves and stems of B. dasyphylla sampled at coal fire area are 903 ng/g and 328 ng/g, and that in the leaf and stem samples collected alongside the main road of the coal field are 131 ng/g and 61.8 ng/g. The result suggests there is atmospheric mercury pollution within the whole coal field area, and the source is the underground coal fire. The pollution level is between typical mercury mine and garbage incinerator. Furthermore, the annual herb B. dasyphylla as a pioneer plant in arid land and desert proves to be a potential biological indicator of mercury pollution for the environmental and biogeochemical study of the prevailing underground coal fire in north China.