A tentative study was conducted in the coal mine fire zone by using the dual-frequency IP method with the assistance of radon measurement. The results of the two methods were well consistent with each other, which was substantiated by exploratory boring. It is shown that at the top of the coal mine fire zone there exists a very obvious abnormal reaction when the dual-frequency IP method is used. The apparent amplitude-frequency rate of the normal value is 2 times that of the background value zone, showing a high apparent amplitude-frequency rate characteristic. The apparent resistivity value is lower than that of the normal area, i.e., only 50％~75% of the value of the normal area. At the same time, the radon value in the fire area is higher than that of other areas. The use of dual-frequency IP method to detect the fire area should be promoted in that it provides a solution to the coal mine fire zones at different depths. This method can also be employed in dynamic monitoring of the coal field fire zone.