Abstract: The outlet bubble evolution and loading mutation during the underwater successive launch have significant impacts on the launch safety. A numerical method for the underwater successive launch of multiple vehicles in a launching tube has been established upon the VOF multiphase flow model and dynamic mesh technology. Studied are the shapes of outlet bubbles and the loading characteristics of adjacent equipment during the first and secondary vehicle launching process. Analyzed is the impact of launching time intervals on the load of the underwater successive launch. The results show that: the underwater continuous launch outlet flow field exhibits asymmetric development characteristics under the action of the structure characteristics of the outlet and the first outlet bubble; and after the secondary vehicle leaves the launching tube, the pulsation phenomenon of the outlet bubbles becomes more complex, resulting in the phenomenon of "double-tube seawater swarming". The maximum impact load on the opening of the launching tube occurs in the contraction stage after the bubble is pulled apart when the first vehicle leaves the launching tube, and the pressure amplitude at the adjacent measuring point can reach up to 800 kPa. During the launch process of the secondary vehicle, the fluctuation characteristics of the load on the opening of the launching tube significantly increase. The launching time intervals have little effect on the load of the the opening of the launching tube. However, with the increase of launching time interval, the pulsating load at the bottom of the launching tube increases. During the process of the underwater successive launch, the adjacent equipment such as the convex membranes and tube cover are subjected to strong pulsating loads. The impact of load on the hull wall is relatively small, and it decreases with the distance from the tube opening; and at the launch interval Δt=3 s, the load increase of adjacent equipment during the departure of the secondary vehicle is small. The research outcome can provide a reference for the safety design and analysis of the underwater launch of the multiple vehicles in a launching tube.