Abstract: As known that flight control design and real-time simulation is very important in the aircraft system, in order to realize linear/nonlinear flight control design and real-time simulation, this study presents the full nonlinear flight dynamic model of tiltrotor aircraft. Primary dynamic equations of the model are developed considering nacelles tilting dynamics. The force and the moment in primary equations are decomposed and calculated by multi-body aerodynamic models, including the aerodynamic effect of rotor wake on the wing/elevator/rudder. Rotor dynamic model is developed based on the blade element theory and the gyroscopic moment caused by nacelles tilting is introduced into the blade flapping dynamics. By the linearization of full nonlinear equations of motion, a family of linear state-space models in the whole flight envelop is obtained. For the velocity control of the aircraft in hover or low speed, the nacelle angle is derived as a new control input. Because the number of unknown parameters is bigger than that of equations, two different algorithms are applied to trim the mathematical model. The results by these trimming methods are in conformity with each other and then the reference transition curve is determined. The results of trimming and linearization derivatives are identical with GTRS (Ground Test Reactor System), so the model is valid.