Abstract: In view of the defects of the isotope radon measurement method, such as large amount of project, long time consuming and easy to be restricted by meteorological factors, the isotopic polonium method for detecting spontaneous combustion source in goaf of coal mine was proposed by studying the related characteristics of polonium which was the daughter of radon. The principle and concrete method of polonium determination were described. At the same time, the method had been applied to the detection of spontaneous combustion in the goaf of Kaida Coal Mine in Yitai Group, Inner Mongolia. The results showed that the isotope side polonium method has the advantages of simple operation, small engineering quantity and less restriction by climatic conditions compared with the isotope radon method. In addition, the polonium method was more reliable and accurate in detecting the fire source, which could effectively reduce the false alarm.