Virtual Reality is an emerging technology in computer visualization. Most of its concepts are useful for a variety of engineering and educational purposes. An important issue in the maintenance of hydropower plants is the understanding of the structure of Hydroelectric Generating Unit (HGU) and its operation mechanism. The applications of virtual reality of HGU are concentrated in recent years. A PC (Personal Computer)-based visualization system of HGU is developed. The physical structures and the internal interactions of HGU in various conditions, even those are invisible in the real world, can be visually demonstrated in detail by this system. It has become a fundamental platform for the condition monitoring, the diagnostic analysis and the staff training in the hydro power plant.