Attitude Estimation for UAV combine Nonlinear Complementary Filter with Integration-Differentiation Observer

State estimation is a key component of the flight control system of unmanned aerial aircraft [1]. In this paper, the nonlinear complementary filter and integration-differentiation observer are detailed respectively. Because of the drawbacks of these observational methods, we propose an observer that combine the advantages of complementary filter and integration-differentiation observer, which can not only obtain the integral and differential of original signals but also has the rectification effect from external sensors. The performance of our proposed observer is verified through simulation based on the hose-and-drogue refueling system. In this system, the attitude angles and disturbances are estimated simultaneously from the angular velocity, and an ADRC attitude controller is designed to compensate the estimated disturbances which get an accurate control.