In order to investigate the influence of initial disturbances on the cavity profile, tail-slapping and ballistic characteristics, the computational fluid dynamics(CFD) model that can be used to solve the coupling equations of rigid body dynamics and unsteady reynolds averaged navier-stokes (URANS) of fluid under different initial disturbances is established based on the CFD program CFX and its expression language CEL. The cavity profile pressure distribution of the projectile tail and ballistic characteristic when the tail-slapping occurs are studied using this model. The result shows that the tail-slapping of the projectile destroys the symmetry of cavity profile; the initial disturbances have slight influences on the velocity and displacements in x-direction but have obvious influences on the vertical displacements; the amplitudes and frequencies of the pitch angle, angular velocity and angular acceleration increase with the increase of the initial disturbances.