To investigate the influences of the empennages on the underwater projectile hydrodynamics, the paper established the numerical models of two high-speed supercavitating underwater projectiles which have identical dimensions except the empennages based on simplified Rayleigh-Plesset equation cavitation model and Shear Stress Transport (SST) turbulence model through solving the Reynolds Averaged Navier-Stokes (RANS) equations of mixture fluid and the mass transport equations between each phase. The projectile′s drag characteristics and supercavitation morphology variations were calculated, analyzed and compared within the identical initial velocity. The results show that the two kinds of projectile models can quickly form stable natural supercavity when moving underwater with a high speed; the impact of the empennages against the cavity surface destroys the original circle cross section of the supercavity and forms a bulge. The drag coefficient of the projectile with empennages is more sensitive to the change of the cavitation number. With the increase of the cavitation number, the drag coefficient of the projectile with empennages increases sharply, and the empennages change the collapse morphology of the supercavity near the tail of the projectile. The cavity collapse at the tail of the projectile causes the drag coefficient fluctuations. The dimensionless length and diameter of the cavity formed by the projectile with empennages are greater than those formed by the projectile without empennages. When the cavity collapses at the tail of the projectile, the variation rates of the dimensionless length and diameter of the cavity for these two projectiles are different due to the influence of empennages.