The application discloses a coaxial helicopter, the cyclic pitch-changing mechanism simultaneously adjusts the pitches of the upper and the lower rotor systems, to make uniformity cyclic pitch-changing adjustment of the upper and lower rotors, and make independent collective pitch adjustment of the upper rotor system; the differential pitch-changing mechanism and the cyclic pitch-changing mechanism jointly act on the lower rotor system, to perform differential collective pitch adjustment of the upper and lower rotor systems. The synchronous rotating mechanism drives the swashplate members to synchronously rotate along with the drive shaft. The application achieves a simpler hybrid pitch-changing control system of the coaxial rotor pitch, a plurality of flight operations of the coaxial aircraft are performed synchronously, and a plurality of flight control modes, such as semi-differential and full-differential in a variable speed or a fixed speed mode, are supported, and thus the present application has wider application space.