When orifice opening of flow under gate through spillways becomes large, large-size radial gates with three radial struts (arms) are normally recommended and have been used in various hydraulic engineering structures/projects. However, radial gates with three arms are easier to have operational failure caused by severe vibrations during opening and closing gate process than those with two arms. In this paper, a finite element numerical model was developed using ADINA software to simulate and analyze natural vibration characteristics of a radial gate with three arms at the Shuhe Hydropower Station using fluid-solid coupling theory. Simulation results of natural vibration characteristics for the gate were also developed without considering fluid-solid coupling. The model results indicate that fluid-solid coupling has remarkable effect on simulated natural vibration characteristics and can not be ignored. Simulated natural frequencies of the same mode are increased with the increase of openings, but the change amplitudes are not significant. This study provides useful information for structural dynamic design of large-size radial gates in order to avoid the natural frequency of radial gate close to the main pulsation frequency of water flow that may cause resonance.