The Large scale distributed system is constructed over long period of time step by step. Even under the construction, on-line operation is started in its system. Afer starting on-line operation, it continuously has to be tested and maintained in various area without stopping on-line operation. On the conventional on-line test technique on Autonomous Decentralized System, the on-line and the test data exist concurrently in the same system. The real-time response of on-line system is not assured.In this Paper, by clustering testlon-line subsystems and controlling data flow among each cluster autonomously, each different type of subsystem is isolated and protects perturbation from the other subsystem. The reliability and real time response of on-line system is assured.