Abstract: A calculation model of water entry and exit of two successively fired projectiles is separately established based on the finite-volume method of NS equation, and the numerical calculation is carried out. The VOF multiphase flow model and Schnerr-Sauer cavitation model are introduced into the numerical method. The evolution law of supercavities and the variation of supercavitating pressure field of water entry and exit of two successively fired projectiles are obtained. Combined with the evolution law of supercavities, the influence mechanism of supercavities evolution process on the velocity attenuation and penetration displacement of two projectiles during water-entering is analyzed. The influence mechanism of supercavities evolution process on the velocity attenuation and the drag coefficient of two projectiles during water-exiting is analyzed. The results show that, for the two successively fired projectiles entering water, the impact load of the secondary projectile is smaller than that of the first projectile in the stage of impact into water. Two cavities induced by the first and secondary projectiles fuse into one supercavity, and the secondary projectile is eventually completely encapsulated by the supercavity. The secondary projectile can catch up and collide with the first projectile, after the collision, the two projectiles move together, and there is a wave phenomenon on the surface of the supercavity. The wall of supercavity with the wave is easy to collapse. For the two successively fired projectiles exiting water, the supercavity induced by the first projectile will stay below the water surface when it meets the free liquid surface, while the secondary projectile flies into the air after it drops the water layer. Under the influence of supercavity peeled off by the first projectile, the secondary projectile can break away from its own supercavity, enter the supercavity of the first projectile, destroy the supercavity, and generate new local supercavity, which is very different from the single supercavitating projectile exiting water.