Abstract: The paper studied the detection of multi frequency radio wave penetration in stope face of underground coal mine, analyzed the field intensity measured by multi frequency detection and tomographic images. The results show that:in detection using multi frequencies, the lower frequency had better penetrability, but can only reflect the geologically abnormal area with big difference of physical property, the higher frequency is sensitive to geologically abnormal area; for medium thick seam in working face 240 m wide, the optimal frequency was 0.158 MHz; when the emission point was close to a fault, the results of detection of different frequencies may be combined to delineate the geologically abnormal area.