Abstract: Taking the heat transfer tube of the steam generator in high temperature gas-cooled reactor (HTR) as the research object, experimental and numerical studies on straight cylinders of round corner square were carried out in this paper. The influences of attack angle and round corner radius on vortex shedding resonance and galloping were studied and the flow characteristics were obtained. The results show that the Strouhal number (St) increases and the velocity of vortex shedding resonance reduces as the radius of the round corner increases. The cylinders with larger round corner radius have lower critical flow velocity of galloping and smaller range of attack angle related with galloping instability. The present study provides important guidance for the design and analysis of outlet pipe bundles of HTR.