Abstract: Abstract: Control valve noise is one of the important sources of noise in a nuclear power plant. The control valve studied in this paper is for controlling of flow rate for the water supply pump for the boiler in a 100 MW nuclear power unit. The flow field in the valve is calculated by CFD method while the far field noise is predicted by the FW H equation. The acoustic characteristics and noise sources of the valve are analyzed. Based on these, the valve exit structure is modified to control the valve noise, by using a drum type exit with small holes drilled in its inner surface. Numerical result shows that the noise sources are mainly the valve discs, and the modification of exit shape is able to dissipate more kinetic energy and turbulent fluctuation, so the noise propagation in the valve is damped and therefore the sound pressure level is lowered down.