Abstract: During the high-speed water entry of a projectile, cavitation occurs, forming a cavity bubble that alters the flow field and subsequently affects the projectile’s motion stability. Our study investigates the characteristics of flow field changes after double-cone projectiles with different head cone angles traverse the free surface. High-speed water entry experiments were conducted by using an electromagnetic launch device, and a numerical simulation model of high-speed water entry was established basing on the overset mesh technique and the VOF multiphase flow model. The validity of the simulation model was verified through experiments, and the flow field characteristics after the vertical water entry of projectiles with different head shapes were obtained. The research findings are as follows: After the vertical water entry of a double-cone projectile, the cavity bubble develops symmetrically. Following surface closure of the cavity bubble, its total length increases while its maximum width gradually decreases. As the head cone angle of the projectile's cavitator increases: during the initial entry phase, the closure point and wetted surface position move closer to the tail; the cavity contour becomes wider; the resistance experienced at the moment of entry and during underwater motion increases, leading to faster velocity decay; the time of surface closure for the cavity bubble is delayed. At the same moment during underwater motion, the length of the tail cavity bubble is longer, while the length of the vortex structures within the water domain is shorter.