The multibody dynamics method is used to accurately analyze the excitation sources of steam turbine mechanical vibration. Based on the analysis results of the excitation sources, the vibration response of the unit under low-frequency excitation is studied, and the Acoustic Transfer Vector (ATV) method is used to study the contribution of sound pressure transmission between the surface and external field radiation of the steam turbine unit. From the perspective of multibody dynamics and the method of fluid structure coupling, the mechanism of vibration and noise generation of the steam turbine unit is comprehensively analyzed, and the typical transmission path of noise is studied. The research results indicate that the rotating excitation source is the main vibration excitation source for the steam turbine unit, the radiation mode of the steam turbine unit in the low frequency range is monopole, and the radiation mode of the steam turbine unit in the medium and high frequency range is dipole. From the directional polar plot of noise radiation, it can be seen that the noise directionality is similar at different heights, and larger values of noise sound pressure levels are obtained in the length direction, indicating strong directionality. The calculation method is of certain guiding significance for the study of vibration and noise reduction of steam turbine units.