Improving hydraulic boundary condition and optimizing structure of hydraulic radial gate are very important measures to suppress the flow - induced vibration of hydraulic radial gate, but these measures, which can be taken only before construction, are not enough for the reduction of vibration. Employing structural control method is a further way to solve the problem. This measure is significant for vibration - absorbing of already existing radial gates. Semi - active control method was proposed to reduce the vibration of certain radial gate installed with magnetorheological (MR) dampers in some key large hydraulic project. The computed results show that MR dampers can diminish flow - induce d vibration of the radial gate effectively under this measure.