Abstract: An attitude estimation algorithm based on fuzzy logic square root quaternion UKF is proposed in order to solve the problems such as the filtering accuracy of target continuous state estimation by discrete sensors observation is too low for navigation solution and the traditional quaternion extended Kalman filtering algorithm can not meet the precision requirement of target attitude measurement． The algorithm takes quaternion as the state of fuzzy logic UKF filter，and the measured time rate is used to complete the time update and measurement update of the filter． The square root covariance form of fuzzy logic is used as the update parameter，which reduces the calculation amount and complexity of the algorithm，and ensures the stability of the value． Taking near-earth satellite as an example， simulation experiments were carried out on Matlab and C + + software． The experimental results show that the pro- posed algorithm could guarantee the accuracy of attitude control for robots and features． It can also track and locate the target in real time and update the measurement，which suppress the problem of attitude error divergence．

Key words: target tracking, quaternion, fuzzy logic, filter estimation