Wall and column structures above the generator layer are primary concerns for studying structural vibration issues of ground powerhouses in hydropower plants. In this article, the influences on free vibration characteristics of a powerhouse when the wall and column structures are connected by steel frames with large stiffness are studied. Furthermore, the influences of sealing structures on stress distribution of powerhouse structures are also studied with design schemes in ANSYS models. The calculation results show that connecting the wall and column structures with steel frames is favorable for the overall vibration characteristics of powerhouse. But the improvement is not remarkable. On the other hand, the position of sealing structures significantly affects the stress distribution, especially stress distribution of volute concrete, of powerhouse structures under designed working loads. These findings provide useful references for the structural design and sealing structure optimization of powerhouses in hydropower plants.