In view of the current situation that the conventional centralized system structure cannot meet the requirement of online extension， online maintenance， and fault tolerance of the system in the operation process of ZPW-2000 track circuit monitoring system， a principle for optimization of the design of the ZPW-2000 rail circuit monitoring system with the autonomous decentralized system（ADS） was proposed. Based on the analysis of the characteristics of the ADS online technique， the detailed optimization plan of the ZPW-2000 rail circuit monitoring system was proposed. In addition， the architecture and elements of the rail circuit monitoring system based on the ADS online technique were designed in detail. The effectiveness of the optimization design method is demonstrated by a case study. The case study proved that the ADS online technique can effectively improve the maintainability， reliability， and flexibility of the ZPW-2000 rail circuit monitoring system， with the obvious advantages of online extension， online maintenance， and fault tolerance.