Abstract: Galloping is a phenomenon of aerodynamic instability, which might lead to severe vibration and failure of the structures in the fluid. The heat transfer tube bundles of the steam generator of high temperature gas-cooled reactor (HTR), which have a square cross-section with rounded corners, are operating in the environment of high-speed helium. In order to study the galloping phenomenon of these special tube bundles, two-dimensional numerical model was established using CFD method based on stability criteria derived from quasi steady state. The data of static hydrodynamic force at different attack angles were obtained to study the galloping stability. The results show that the rounded corner has great influence on the stability of structures, which will reduce the fluid drag coefficient significantly and therefore reduce the critical flow velocity of the structure’s galloping. The structures with larger radius of the rounded corner have smaller range of attack angles of the galloping instability. The present study provides important guidance for the design of heat transfer tube bundles of HTR.