Abstract: We developed rotary drilling measurement system to accurately position gas drainage drilling positions and eliminating gas drainage blind area. The system includes non-magnetic rod, measuring probe and synchronizer. Azimuth is measured by the magnetoresistive sensor. Inclination measured by the acceleration sensor. Finally, we got the actual drilling trace by calculation. Field application shows that all drill holes were presented trace deviation. Deviation was different because of different construction techniques and geological conditions. We got gas drainage blind area by statistics drilling trace deviation which eliminated drainage blind spots and ensured safe production.