Since the conventional quad rotor UAV is limited by the slow flight speed, short battery life and fixed wing aircraft cannot VTOL and hover, a small QTR (Quad Tilt-Rotor) UAV was designed. The dynamic model of QTR was constructed. Considering the characters of attitude control in transition period, design the attitude controller based on robust servo LQR control theory. Then a control maneuver for the QTR transition from vertical mode to horizontal mode was proposed. And control method was verified by the simulation, comparing with the traditional control method. The simulation results show that the UAV can not only take into account the abilities of traditional quad rotor UAV, but also can fly long distances like the fixed wing aircraft.