In water conservancy projects, radial steel gates play an important role in the discharge process. According to the accident cases, it was found that the radial steel gates were often damaged due to the instability of the support arm. The arrangement of support arm connection systems can enhance the stability of the gate to a certain extent, but currently the connection systems are varied without clear standardized arrangement method. Taking the emersed three-arm radial gate as the research object, we studied the influence of different forms of connection systems on the static and dynamic characteristics of the gate by means of joint simulation of CAD-CAE. The results indicate that the arrangement of the connection system can significantly increase the stiffness of the gate, thereby changing the stress distribution of the gate structure and reducing the maximum stress. It is found that internal web and diagonal members of the support arm have a significant improvement effect on the static and dynamic effects of the gate, and priority should be given to their arrangement. In the numerical simulation, the components of the support arm connection system have a significant impact on the simulation results. Therefore, it is necessary to avoid overly simplifying the support arm connection system as much as possible in the verification of the support arm of the radial gate using the spatial finite element method. The research results can provide a reference for the arrangement and finite element calculation of the support arm connection system of radial steel gates.