Abstract: To monitor and assess effect of coal fire in Wuda Mine of Inner Mongolia, taking ASTER thermal infrared bands before, during, after extinguishing coal fire and during monitoring period as data sources, coal surface temperature was inverted by TES algorithm and coal fire areas during four time phases were extracted based on self-adaptive gradient threshold method. By comparing fire areas in 2008 with aerial referenced fire areas in 2009, the accuracy of fire areas identification was 71.4%. According to developing states of coal fire between 2008 and 2015, results revealed that coal fighting-fire project achieved good effect and coal fire areas changed into sporadic distribution from concentration due to dramatically shrinking of 2.5 km² coal fire areas from 2008 to 2013. However, during 2013 and 2015, coal fire areas increased 0.3 km² and became more concentrated from discrete forms. And residual fire size of 1 km² indicated that more extinguishing fire technologies needed to be strengthened in the future.