During the LNG ship tightness inspection process, the helium test effectively detects leaks in the corrugated plate of the main screen wall. To enhance the detection efficiency of weld defects in these corrugated plates, a testing device equipped with multiple suction guns arranged in parallel along the main pipe has been designed. This paper analyzes the helium test line based on tightness testing and investigates the impact of various factors on the flow field of the main pipe through finite element simulation. These factors include the number of parallel branches, the length and inner diameter of the branch pipes, and the pressure changes at the inlet and outlet. The study identifies key factors affecting the flow field in the development of the multi-branch parallel workpiece. Results indicate that increasing the number of branches has minimal effect on the velocity and pressure at the outlet pipe near the center axis, but it does affect the velocity and pressure near the pipe wall. Furthermore, the presence of branches reveals an optimal branch length that maximizes the flow velocity at the outlet near the tube wall.