As an aircraft with special configuration, the tilt tri-rotor UAV combines the advantages of helicopters and fixed-wing aircrafts and has the operating modes of the two at the same time. Whereas, the engine nacelle should be controlled in the transitional mode, which brings the problem of manipulation redundancy, and neither manipulation approach is fit for use alone. In order to solve the problem of aircraft manipulating redundancy of the tilt tri-rotor UAV in the process of nacelle tilting in the transitional mode, an appropriate dynamic model of the tilt tri-rotor in the transitional mode is built, and a new tilting control method based on fuzzy control is proposed. Through the experimental analysis and the comparison with the traditional manipulation strategy of the tilt rotor aircraft in the transitional mode, it is found that this method can solve the problem of longitudinal height control of the tilt tri-rotor UAV in the transitional mode, so that the tilt tri-rotor UAV can implement a smooth and efficient flight in the transitional mode.