Abstract The scope of O.A. application is enormous. Many mainframe or mini-computer manufacturers provide various program tools and packages to help customers to develop their O.A. system. Since the applied requirements of each O.A. system is not the same, therefore the structure would be different. In some circumstances, it's not economic to use a mainframe or minicomputer to do the works. This Paper proposed that the performance of a chinese-based PC linked with bus will approach the behavior of large computer under the condition that the quantity of local processing of a O.A. job is much greater than the quantity of communication processing. Since the tasks of O.A. jobs can be classified into two parts: local processing part and communication processing part, meanwhile, we discuss which network structure meets our requirements for various O.A. applications.