Aiming at the serious coupling interference problem between the channels of the composite coaxial high-speed helicopter, this paper studies the maneuvering modes in different flight phases, and adopts the idea of serial control to design the inner-loop ADRC attitude controller and outer-loop velocity/position non-singular terminal sliding mode controller, respectively. Considering the switching problem of control surface during the transition process, a control allocation strategy based on the FSQP optimization algorithm is adopted to realize the optimal mapping between the virtual control quantity and the actual manipulation quantity. The ADRC-based controller can realize fast tracking for given instructions, overcome the uncertainty of disturbances, and solve severe coupling interference between channels; the proposed control allocation strategy effectively solves the coupling problem seen in the longitudinal and lateral channels.