Abstract: There are many practical problems in the spontaneous combustion area of small coal mines coal mine in Shanxi Province, such as many fire sources and wide distribution range, hidden fire source location, difficult to accurately detect, many air leakage channels, and difficult to prevent and control. In order to accurately detect the location and range of fire source, firstly, The detection mechanism of spontaneous combustion area detection method is studied. Based on the basic theory of radon measurement method and magnetic method to detect fire area, the detection principle of ground ' radon measurement-magnetic ' joint technology is proposed to accurately detect the location and range of small kiln fire source. Secondly, FD213 alpha spectrum radon measuring instrument and GSM-19 T magnetometer were used to collect the hidden fire source data of small kiln on site. The ground ' radon measurement-magnetic ' joint technology was used to process and analyze the collected data, and the location and scope of the hidden fire source of small kiln were comprehensively delineated. The location of the fire source was verified by using underground temperature measurement and gas measurement boreholes, combined with the preliminary detection results and the distribution of underground roadways. Finally, the borehole grouting technology is used to control the fire area, and the combined technology of beam tube gas monitoring and re-measurement of radon method is used to detect the effect of fire area control. The test results show that the location and range of the hidden fire source delineated by the ' radon-magnetic ' joint technology are successfully verified by the results of downhole temperature measurement and gas measurement drilling. The area of the hidden fire area delineated in this test is about 213 m². The cumulative filling material of drilling grouting fire area treatment is about 1862 m³; the detection of the treatment effect shows that the internal index gas CO concentration in the fire area is delineated.