Water hammer is produced due to the fast shut of electricityhydraulic ball valve while underwater vehicle pressure water pipeline system suspends working. In this paper, water hammer in the pressure water pipeline is numerically simulated by the Flowmaster software, and various factors affecting the water hammer are studied. Accordingly, methods are developed to prevent the water hammer in the underwater vehicle pressure water pipeline, which is valuable to reduce vibration and noises produced by water hammer in the underwater vehicle pipeline and is practically significant to improve the underwater vehicle stealth and combat capability.