In the attitude measurement system, Unscented Kalman filter algorithm based on quaternion has been developed according to the problems of noise and drift by the three-axis MEMS gyroscope, three-axis MEMS accelerometer and three-axis MEMS magnetometer. According to the principle of strap down inertial navigation, the paper developed the attitude-updating algorithm based on the quaternion, the mathematics model of airborne platform attitude angle has been established based on the drift attitude error of the velocity gyroscope. Simulation results showed that the algorithm can solve the low accuracy, easily lead to divergence, and easily be interfered problems in use of measurement the attitude of airborne platform existing in MEMS inertial device, and the algorithm raised the accuracy of the pose estimation.