The coaxial tilt-rotor craft is a high-speed rotorcraft along with deployable fixed-wings. A mathematical model is built for analyzing the performance of coaxial tilt-rotor in helicopter flight condition, transition condition and fixed-wings airplane flight condition. Firstly, the application of the model shows good agreement with the experiment from wind tunnel test of coaxial tilt-rotor in axial state and coaxial rotor in forward flight. Then, the method is studied by analyzing the obtained results of the variation of performance parameters, the distribution of induced velocity, the change of overlap area and interaction factor in transition condition. The calculated results show that when the tilt angle increases at constant flow, the thrust coefficient of coaxial tilt-rotor decreases, the power coefficient increases first and then decreases, the overlap area and the interaction factor of upper and lower rotors both increase.