Abstract: A trajectory measuring instrument for mine while drilling based on magnetic sensor and MEMS acceleration sensor is designed, the design of measuring unit of trajectory measuring instrument is mainly discussed. The measuring scheme of measuring earth magnetic field and gravity field by using magnetic sensor and acceleration sensor is given. The low power consumption mode of the instrument is studied, and the design scheme of time calibration by using real-time clock chip is discussed. Through precision test and application examples, it is proved that the trajectory measuring instrument has the characteristics of high precision, low power consumption and small size and can fully meet the requirements of drilling trajectory measurement in actual drilling technology.