Abstract: A mine-used Omni directional borehole inclinometer based on the PNI magnetic induction sensor and SCAl00T accelerometer was developed. The whole structure of the system, measuring principle and the sensor circuit were introduced in detail. Meanwhile, the system errors and its error sources were analyzed, the model of error compensation and its calibration method were also proposed. The experimental results show that Omni directional borehole inclinometer based on PNI magnetic sensor has the advantages of small size, high precision and high reliability, meeting the project requirements.