This paper describes the autonomous flight of a quad tilt-rotor UAV at a constant altitude. The quad tilt-rotor UAV is one of the advanced multirotor UAVs that enables independent control of position and attitude. It can fly horizontally without changing its attitude, which can not be realized by the conventional multirotor UAVs. By virtue of the above features, an autonomous flight system can be achieved with a simpler and lighter two-dimensional laser range finder. This paper first reviews the performance of the existing SLAMs in our experimental conditions, and the flight experiment is carried out for validating the developed system.