To solve the problems of control surface redundancy and severe channel coupling of the tiltrotor aircraft in its transitioning process,we studied the rudder distribution strategy and the control channel switching strategy of the aircraft in the transition mode,and designed an attitude controller based on active disturbance rejection control.According to the characteristics of flight control,the structure of the active disturbance rejection controller was optimized,the order of the extended state observer was reduced,and the differential output of the tracking differentiator was used as the attitude angular rate instruction to simplify the structure of the attitude controller.Through the whole-envelope flight control simulation of the tiltrotor aircraft,the validity of the control system and the rationality of the rudder distribution strategy and the channel switching strategy are verified.