A computational fluid dynamics method has been applied to simulate the exhaust gas flow and the additional thrust during a missile launching from concentric canister launcher. The unsteady, axisymmetric Reynolds-averaged Navier–Stokes equations with renormalization group k-ɛ turbulence model are numerically solved here. The dynamic mesh method is utilized to simulate the movement of the missile. Computational fluid dynamics results show that the additional thrust is an important thrust and fluctuates with the movement of the missile for launching from concentric canister launcher. The mechanism for producing and influencing the additional thrust is typically relevant to the choking states of exhaust gases at the inlet and outlet of the annular tube of concentric canister launcher, responding to the jet impinging on the bottom of the launcher, the approximate wall jet, and the friction effect in the tube.