Abstract: In this paper, a kind of azimuth measurement technology for seafloor observatory station is proposed based on 9-Dimension of Freedom(9-DoF) Attitude and Heading Reference System(AHRS). It uses Kalman filter to estimate orientation and Gauss-Newton iteration method to get measurement state, and then combines gyroscope, accelerometer and magnetometer data from MEMS sensors to make a detection. For Kalman filter, the system error, which is sensitive to changes in temperature, and the measurement error are both estimated. Finally, the system is tested under quasi-static conditions and compared with the orientation obtained with non-magnetic turntable. The results show an improved performance:the error is less than 1% and low angle bias of pitch and yaw direction is less than 2 degrees per hour.