Abstract: Measurement of while-drilling trajectory in underground coal mines is crucial for gas drainage and water hazard prevention and control. However, conventional borehole trajectory measurement systems rely on magnetic sensors to measure the azimuth angle; their measurement accuracy is susceptible to interference from the ambient magnetic field, and they must be equipped with high-cost non-magnetic drill rods. Aiming at the problem that magnetic sensors are vulnerable to magnetic interference in underground coal mine while-drilling trajectory measurement, resulting in large azimuth measurement errors, a while-drilling trajectory measurement system utilizing gyroscopes for azimuth measurement is designed based on inertial navigation theory, which fundamentally eliminates the influence of magnetic interference on borehole trajectory measurement accuracy. According to the principle of the strapdown inertial navigation system (SINS), a three-axis gyroscope is adopted inside the measuring probe to sense the Earth’s rotational angular velocity for azimuth calculation, and accelerometers are used to perceive gravitational acceleration to measure the inclination angle and tool face angle of the drilling tool. Meanwhile, a multi-stage damping structure is designed to reduce the impact of while-drilling vibration on inertial navigation devices. Intrinsically safe circuits complying with underground coal mine explosion-proof requirements are developed, enabling the measuring probe to meet the high-precision while-drilling measurement requirements in complex underground borehole environments in terms of dimension, shock resistance and explosion-proof performance. The system adopts the data transmission technology of central cable-through drill rods to realize two-way communication between the measuring probe and the orifice computer. The borehole trajectory curve is fitted by combining drilling tool attitude data and borehole depth information. Experimental results show that the azimuth measurement error of the measuring probe is less than ±1° under laboratory magnetic interference conditions, with a time drift stability better than 0.1°/h. In field actual drilling tests, the trajectory measured by the proposed SINS-based mine while-drilling trajectory measurement system presents a consistent variation trend with the re-measured trajectory of the YSX-2000 mine wired while-drilling measurement device. This verifies the reliability of the system under complex while-drilling working conditions, providing an effective and reliable solution for high-precision borehole trajectory measurement in magnetic interference environments during directional drilling in underground coal mines.