This paper investigates the physical mechanism of corner-cut on aerodynamic stability in a rectangular bluff body by using Large Eddy Simulations. In corner-cut case, the flow attaches at 1^st and 2^nd leading edges and high frequency components of velocity fluctuation are more active at the trailing edge area, therefore they enhance or stimulate the reattachment tendency of shear flow on side surface and keep the Karman vortex form further from the rear side of the bluff body. As a result, the size of wake structures is much smaller, the recirculation length is longer, therefore, the value of drag coefficient and Strouhal number changes significantly.