Presently, the strapdown inertial system has become one of the most important research directions of inertial technology, attitude algorithm is an important part of SINS algorithm, and the algorithm's accuracy will directly affect attitude control. In this paper, the scheme which adopts three-axis MEMS gyro for attitude detection and rolling angles resolved by two-axis magnetometer signals for gyro accumulative error correction was proposed. The algorithm of gyro and magnetometer calculating missile's attitude was simulated. The results show that the scheme has higher precision than the scheme which only uses gyro signals and is used for improving the precision of attitude angles.