In this paper, a finite element model (FEM) for inlet control valve was built and the structural modal analysis was performed to get the Eigen-frequencies of the valve. The valve plug as well as the stem together with piston rod and spring block were analyzed separately. Some peak frequencies of the main inlet control valves were obtained at the 2% lift case during warm-up stage on a nuclear power plant. The dynamic flow field as well as the steam forces were obtained by computational fluid dynamic (CFD) calculations with DES turbulence model. In order to clarify the cause of the valve vibration, the natural frequencies were compared with the test data to indicate that the frequency of certain rocking modes may coincided with the test results. What’s more, the peak frequencies of the dynamic steam forces from CFD simulations were also compared with the rocking modes of control valve to identify the mechanism that cause the vibration at certain frequencies.