Abstract: The aerodynamic characteristics and flow field of rectangular cylinder with rounded corner are very complex. To further understand the Reynolds number (Re) effect of rectangular cylinder with rounded corner, the large eddy simulations (LES) of flow around a 4∶1 rectangular cylinder with rounded corner under different Res are carried out, which are based on the computational fluid dynamics (CFD). The aerodynamic coefficient, Strouhal number (St), wind pressure coefficient and flow field under different Res are comprehensively studied. The results indicate that the surface pressure and time-averaged flow field are sensitive to Re when Re ≤ 4×10³; however, they are insensitive to Re when Re > 4×10³. In addition, when Re ≤ 4×10³, the root mean square of lift coefficient and the mean drag coefficient increase and then decrease with Re, and they reach the maximum at Re = 1×10³. Nevertheless, St first increases, then decreases and finally increases, and its maximum and minimum are at Re = 2×10³ and 4×10³, respectively. With the increase of Re, the recirculation length first decreases and then increases, and the center of the wake vortex moves backward gradually.