In order to study the mechanical properties and the dynamic performance of torque converter, to reduce the vibration and noise during the operation and to improve the stability, a 215mm hydraulic torque converter is taken as the research object, and modal analyses are performed based on the fi-nite element method. The weak parts of the impeller structure are obtained after calculating the mod-els of the impeller and turbine without prestress. The variation of the modal frequency of the turbine and impeller are obtained under different prestress conditions by calculating different rotational speeds of the transmission shaft. The fundamental frequencies of the impeller and the turbine in-crease by 0 . 43％ and 4 . 82％ respectively when the rotational speed ranges from 100 rpm to 4500 rpm. The results of the present research indicate that the modal frequencies at different speeds are similar to the fundamental frequencies of the structure. Therefore, it is possible to estimate the vibration characteristics of the structure and optimize the structural design by numerical modal analy-sis in the static state instead of the dynamic state.