The authors developed one method and tried to make clear its suppression mechanism. By using a plate that is placed to normal to the surface of the body at an optimum position, the separation flow from the leading edge is forced to touch the tip of the plate. The method was named by one of authors, as Separation Interference Method (SIM). The detail of this method and the suppression mechanism on the aerodynamic vibrations are described in the present paper. As a result, it is shown that circulatory flow between 1st separation point and 2nd separation point is very important for SIM. In the present paper, it is concluded that the mechanism of SIM possesses the same effect on both the square prism and the rectangular prism with re-attachment of separation flow. Furthermore, it is made clear that SIM is also effective in turbulent flow as well as in smooth flow.