An adaptive backstepping fault-tolerant flight control design is proposed for an attitude system of unmanned aerial vehicle (UAV) with external disturbances and multiple actuator faults. The allowable actuator failure is unknown, and the total occurances of faults can be unlimited. With the advantage of not requiring additional fault detection and estimation mechanism, the designed adaptive backstepping controller compensates for the effects of actuator failure and achieves attitude tracking. It is proved by Lyapulov analysis that all signals belonging to the closed-loop system are globally bounded, and the output tracking error of the system can be exponentially converged to an infinitesimal origin field. Finally, simulation results are given to demonstrate the effectiveness of the proposed strategy.