Abstract: The main steam isolation valve (MSIV) in nuclear power station is one of the most important items of nuclear equipments in Localization Process project, which requires strict technical standard and high safety coefficient. During the operation of some nuclear power stations, MSIV gets the problem of vibration and noise due to airflow, which leads to the damage of valve accessory. In order to find the reason of vibration and noise, the method of numerical simulation to calculate the inner 3D on flow field of MSIV was used. The results of numerical analysis match with the on-site measurements.