Abstract: For problems of low positioning accuracy and high cost existed in current underground personnel positioning system, a personnel positioning system in coal mine underground based on MEMS sensor was designed. The system uses MPU9150 inertial sensor to obtain measurement data and takes CC2530 as the main control chip to collect and process data. It combines with pedestrian dead reckoning (PDR) algorithm and through existing underground WiFi base station to realize accurate positioning for underground personnel: it uses an expression that combined the variance of the walking frequency and acceleration to determine step length, and uses the quaternion method to estimated pedestrian orientation angle, uses extended Kalman filter to correct the original data, so as to obtain specific location of underground personnels. The experimental results show that the positioning error of the system is less than 2.2 m in 100 m, which can achieve high accuracy of personnel positioning in coal mine underground.