Abstract: To solve a problem that systematic errors accumulated with time in the strapdown attitude determination system for the trajectory correction,a low-cost magnetic-inertial attitude measurement system composed of two-axis magnetometers and MEMS gyroscope was proposed. The geomagnetic information were used to correct attitude error from MEMS gyro and geomagnetic. Geomagnetic signals were devoted to the rotation vector in calculating attitude. A principle prototype was designed and fabricated, and it was tested on two-axis turntable. The determination system can effectively suppress attitude error caused by the gyro drift. This paper proves that the attitude determination system can be reliably used for trajectory correction on some condition.