Throughout the last decade, more and more attentions have been focused on the reliability of flight system in the aircraft control.In this paper, a high-reliability attitude stability control system was designed for a novel VTOL unmanned aerial vehicle (UAV), a quad-rotor aircraft.In order to compensate for the influence of the actuator fault to the aircraft control, an active fault-tolerant control system was introduced into the attitude control system.This scheme was composed of two components:A robust fault detection module using the model-based observation approach and a reconfigurable controller.The robustness and stability of the fault-tolerant control scheme were also analyzed theoretically.The availability of the proposed scheme was verified through numerical simulation.