Targeting the attitude tracking control of hypersonic flight vehicles (HFVs) under model uncertainties and external disturbances, a fixed-time-synchronized controller (FTSC) is proposed. The 6-DOF attitude tracking control of HFVs is a great challenge due to the extreme flight environment, the complexity of hypersonic aerodynamics, and serious coupling. The FTSC is proposed with a norm-normalized signum function. By ensuring ratio persistence between state variable components, fixed-time synchronization is achieved, which brings the controller a smoother converging scheme, and the impact of disturbances between coupled channels is inhibited. In addition, model uncertainties and disturbances are handled with an extended disturbance observer, with a rapid converging procedure that synchronization properties proceed. Stability analysis is established with Lyapunov techniques and the fixed-time stability theory. Lastly, numerical simulations are carried out to show the feasibility and priorities under comparison.