2. Xi'an Ｒesearch Institute of China Coal Technology ＆ Engineering Group，Xi'an 710000，China

threatening to mine in actual production and verify the effectiveness of borehole radar in underground detection of coal mines，the authors use gprMax2D which is based on the finite difference time domain ( FDTD) method to simulate

borehole radar data． Horizontal borehole model with different frequencies under different coal thicknesses，slanted borehole different dip angles，faults，fracture zones，collapse columns and dirt bands models were built and

corresponding simulating results were obtained． The results show that borehole radar can identify the position of the roof and floor，and find the abnormal geological structures effectively． When the center frequency of the radar is from 50 MHz to 600 MHz，better detection results will be obtained． The resolution increases with the increase of the frequency． Slanted borehole has little influence on the identification of roof and floor． Faults，fracture zones，collapsed

columns and dirt bands have shown their own characteristics in simulating results． These characteristics provide references for the interpretation of the radar profile in actual production． In summary，it is feasible to use borehole radar to identify the position of coal seam roof or floor and find the abnormal geological structures．