Inertial measurement method is widely used in attitude determination of lowcost civil MUH(Mini Unmanned Helicopter).But the dirft of gyroscope and the kinematic acceleration affect the accuracy of estimation.This paper designed a Kalman filter based on quaternion.According to the gyroscope and accelerometer signal,fusion the attitude of MUH.And designed adaptive covariance matrix of measurement noise to improve the fusion accuracy.Get stable and highaccuracy attitude information for stability augmentation system. Experiment data shows that the method can effectively solve the problem of attitude determination of MUH.