Abstract: Pressure vessels have different specifications of connecting tubes. When the connecting tubes are under internal pressure, they will bear complex loading, such as bending moment, torque and so on. That will complicate the stress of the tubes, which cannot be calculated by the conventional design method. This article uses the finite element method to analyze the stress induced by the bending moment of the tube on the connection of the connecting tube and the elliptical head. It also provides references for the opening reinforcement calculation of connecting tube under similar load condition.