Abstract: According to special underground working environment, the paper researched relationship between overlapping loop device with different length, different shapes and different number of turns and turn-off time and quality of received signal. And got conclusions as follows: the turn-off time is less influenced by shape of the overlapping loop and number of turns of receiving coil, is more sensitive to change of area of the overlapping loop and number of turns of transmitting coil which shows a linear increase relation. In limited underground construction space, increasing area of the overlapping loop and number of turns of the receiving coils can obviously improve and guarantee quality of the received signal. Circular overlapping loop device can obtain the maximum receiving area in the same circumference. Increasing number of turns of the transmitting coil does not contribute to improvement of quality of the received signal.