A rapid deployment transition control method is proposed for the flight deceleration and attitude adjustment control of a gun-launched coaxial twin-rotor vehicle in the transition process. The Newton-Euler equation is used to establish the transition control model of the coaxial twin-rotor vehicle, and to study the deceleration and attitude adjustment control scheme strategy during the transition by combining the working principle of the co-axial twin-rotor vehicle and parachute. The internal and external loop controllers are designed using the adaptive backstepping control algorithm, and the position, velocity, and attitude states during the transition process are controlled using force and torque as control inputs. The accuracy of the parachute and vehicle transition model of the coaxial rotor vehicle with parachute were verified through the simulation analysis of ballistic trajectory, position and attitude. The results show that when the projectile reaches the high point and starts to disperse, the deceleration parachute is opened after 5.3 s. Under the joint action of the deceleration parachute and the rotor maneuvering mechanism, the attitude angle and speed are quickly adjusted by the parachute aircraft conversion control algorithm, which significantly improves the deployment speed.