In order to improve aerodynamic drag of projectile with base cavity, drag reducing effect got from projectiles with different base cavity was investigated. Based on Navier-Stokes (N-S) equations, distribution of flow field parameters and aerodynamic drag was obtained by numerical simulation method. The effect of base cavity with same length but different shape on flow field and drag reduction were discussed. The results show that the recirculation region, which is caused by the base cavity and located inside the cavity, plays a pivotal role in reduction of the drag. In the paper, the projectile with a “contraction" shape has the minimum aerodynamic drag.