Recently, system needs of growing large-scale systems including heterogeneous functions and operations are increased. Assurance system that achieves high reliability and high availability is very important for such systems. In order to realize assurance system, we developed the assurance technology based on ADS (Autonomous Decentralized System). When a growing large-scale system changes or grows, its reliability may be lowered. In this paper, we clarify the risk factors which lower the reliability and quality of a growing system when the system is modified. We will then examine the methods to eliminate or ease those risk factors, and propose adaptable assurance technology that can minimize the risk under restrictive conditions such as cost, resource, periods, etc. We also describe ATOS as an example that was applied the assurance technique and its effectiveness as really changing and growing system.ATOS; Autonomous Decentralized Transport Operation Control System.