To investigate better the coupling between the flexible barrel and the bullet during the artillery firing process, a method was presented by introducing the virtual substance, in which the force was passed indirectly through an analog barrel that is composed of virtual substances. And the rigid-flexible coupling dynamics equation of the projectile-barrel system including virtual substances was derived. Taking an artillery for an example, the system model was introduced, then the comparative curve between the experimental data and the calculation result under the same firing condition was obtained. The comparison shows that the present model can transfer the projectile-barrel collision force and reflect truly the law of projectile motion, which provides reference for artillery launch dynamics.