For the maintenance of the Nuclear Power Plants (NPPs) equipment, in order to ensure the safety of personnel and equipment during the maintenance, it is necessary for the operators to set the corresponding isolation boundaries for them and and conduct manually mapping on paper flow charts before the implementation of the maintenance. There are many disadvantages for this manual mode such as high ability requirements of operators, time-consuming, laborious and prone to human errors. This challenges the safety and economic operation of the NPPs. In order to solve this problem, this paper combines the design and operation experience of the NPPs, takes the digital system flow charts as the design input, the isolation rules are studied, and the automatic identification method of equipment maintenance isolation boundaries of NPPs is proposed on the basis of these rules. The research results of this paper can be widely used for all the NPPs with digital system flow charts. Especially for the design stage of the new NPPs, the research results can be used to build data model and integrate into the data center to realize data sharing, which provides the core data basis for the subsequent development of the whole process of the NPPs isolation management, and has the milestone significance for the digital transformation of the NPPs.