Based on numerical virtual flight technology, unsteady N-S equations and 6 DOF equation of motion were coupling soluted using moving chimera grid. A method was developed to estimate projectile stability, and it could consider the effect of unsteady aerodynamic characteristics. Through the numerical simulation of the slandard model for a typical external store release and the standard model of M852 bullet of BRL. The results showed that the numerical method was accurate and available, and it could be used in numerical virtual flight simulation. Finally, the virtual flight simulation of a mass simulated projectile was carried out, and the numerical result gave dispersion and flight stability assessment conclusion under different disturbances.