Abstract: The quality of a water trajectory decides whether the sub-launched missiles can be launched successfully. The attached cavity on a missile due to velocity increase adds to the indeterminacy of fluid forces, and it enhances the difficulty of water trajectory design. According to the features of a sub-launched missile navigating in water, experiments were carried out to investigate the cavity profile and force characteristics using the ventilated cavity method. The effects of the angle of a conical head on the cavity shape and the fluid dynamic features were studied, with the conclusion that the re-entrant jet effect and the free attack angle become more distinct as the cone angle increases. Referring to the shape-design theory of supercavitating vehicles, a series of truncate conical heads were designed. The experiment results have validated the improved stability performance of the new models, which can be referenced by sub-launched missile underwater ballistics design engineers.