In the process of underwater continuous vertical launch of the multi-vehicles in single launching tube， the gas overflowing between the built-in neighbouring launch tube interacts with the water to form a complex form of gas bubbles， and the expansion-contraction characteristics of the gas bubbles affect the flow field of the underwater continuous launching. In order to investigate the variation laws of the pressure field near outlet and its impact on the fluid load characteristics during the continuous launching process of the vehicle， numerical simulations are conducted using the VOF multiphase flow model and dynamic mesh technology controlled by user-defined functions， with a launching interval of 2 seconds for the continuous launching process of two vehicles. The simulated results show that when the first vehicle leaves the launch-tube， going through 1s time course， the pulsation of the launch outlet pressure field is significantly weakened， and after the secondary vehicle leaves the cylinder， the launcher flow field shows an obvious asymmetric distribution； The outlet bubble formed when the first vehicle leaving the launcher，which creates an air curtain environment on the subsequent vehicle launch channel， it reduces the axial load F_x of the secondary vehicle and also reduces the load of the adjacent equipment of the barrel mouth， but the asymmetric development of the outlet bubble leads to violent oscillations in the deflection force and deflection moment of the voyage， which will affect the initial trajectory of the vehicle. The research results may provide reference in the field of demonstration of underwater common frame launch scheme for engineering application.