The paper studies the modeling of the aircraft-rocket coupling dynamics during air launch of the transporter-mounted rocket. The modeling aims at two stages. In the first stage， the rocket is fixed in the cabin of the aircraft， so they constitute a whole， which is treated by single rigid body mechanics. In the second stage， after the rocket is unlocked， it moves along the launch tube in the cabin. While sliding outside， the aircraft and rocket constitute a coupled system of two interacting rigid bodies. A dynamics model is established using Newton-Euler method for the two rigid body systems. When the aircraft launches the rocket， the throttle and elevator are fully deflected， so its pitch angle is increased while accelerating forward. The rocket will slide outward along the launch tube in the cabin under the action of its own gravity component and inertial force till separating from the aircraft. Finally， through numerical simulation， the paper analyzes the change of some important mechanical variables of the aircraft during air-launch， verifying the feasibility and safety of the aircraft’s control strategy. The analysis results provide the data references for China’s air-launch rocket technology in the future.