<p>This paper investigates the predefined time tracking control of a quadrotor UAV in the presence of input saturation, external disturbances and tracking error constraints. In order to realize the predefined time bounded of position and attitude tracking errors, a tan-type barrier Lyapunov function is introduced, and the continuous piecewise function is used to avoid the singularity of power exponents. Considering the saturation limit of the control input, the auxiliary system is proposed to compensate the influence of input saturation. Moreover, a predefined time disturbance observer is utilized to accurately estimate the uncertainty caused by external disturbances. Using the presented observer, the observation error converges within a predefined time. The theorem analysis shows that the controller ensures the tracking error converges to a specified interval in a predefined time without violating the tracking error constraints. Simulation comparison results verify the effectiveness of the proposed control scheme.</p>