After reviewing the major motivations for the application of a computer in a BWR Plant, the concept of an integrated hierarchical computer complex, containing distributed control and data processing features, was made. The computer complex, which has three major components, a large scaled database computer system, distributed computer, and communication network, is classified into three levels depending on the scale of the computer system. On the other hand, the computer complex is also divided into two categories, depending on the functions of the computer system. One has the supervisory and control functions, the other has the data processing and management functions. The scope of this system ranges from the overall station management to the local control. The integrated hierarchical computer complex can provide an efficient, flexible, and reliable support in the management of the BWR Plant.