Abstract: The underground electromagnetic wireless measurement while drilling (EM-MWD) instrument is developed. According to the characteristics of underground EM-MWD, the transmission frequency can be set as 6.25 Hz and 12.5 Hz, and the encoding method adopts power-saving differential pulse position modulation (DPPM). The transmitter is designed with power saving mode and hibernation mode to extend the battery time. The EM-MWD isolation antenna of φ73mm is coated with multi-layers emery to improve the wear-ability, and the EM-MWD receiver uses RLS adaptive filter to improve ability of anti-interference performance. Experiments results show that the communication distance of the developed EM-MWD instrument is more than 310 m, the power saving mode and hibernation mode of the transmitter work effectively, and the mechanical strength and wear-ability of the isolation antenna can meet the requirements of the underground coal mining.