Satellitestend to be micromation in future. Itis necessary to investigate small, cheap self-contained navigation system with moderate precision. According to measuring data of three-axis magnetometer in the body frame, the attitude of the satellite in low orbit can be determined through Kalman Filter. Combining the dynamical model of satellite's attitude with the standard model of the geomagnetic field,the filter model and arithmetic used to determine the attitude of the satellite are presented. The result of simulation shows that the project of three-axis magnetometer attitude determination has a certain precision, which has an applicable future in the self-contained navigation system with moderate precision attitude determination.