Aiming at the difference between the coaxial rigid rotor and the conventional rotor, the aerodynamic models of coaxial rigid rotor are built in terms of rotor flapping, pitch control and induced velocity. The flapping movement function of the coaxial rigid rotor is introduced based on the concept of equivalent flapping. The pitch control motion fitting with the flapping frequency of coaxial rigid rotor is modeled based on the concept of control phase angle. The induced inflow velocity of the coaxial rigid rotor is modeled by using the interference factor. With the flight dynamic models mentioned above, the trim characteristics of pure-helicopter mode with the example of XH-59A helicopter are analyzed, and the models are verified by the flight test data. Comparison of the trim characteristics between coaxial rigid rotor aircraft and conventional single rotor helicopter is performed.