Abstract: After a single net-node failure in the nuclear power plant, the conservative decision must also consider the net node failure at other locations and make an enveloping risk analysis. Based on the modeling and analysis of Distributed Control System（DCS） network structure and control logic data of a nuclear power plant, the calculation method of the physical path of network signals and the judgment rules of signal redundancy are given, the failure probability of the remaining network nodes is calculated by constructing the state transition matrix under single node failure, the network signal risk analysis and evaluation under single or superimposed failure are carried out, and finally the risk control and improvement suggestions are given for the identified high-risk network signals. This model and analysis method have been realized by computer software, which can quickly identify design defects such as false redundancy and unreasonable layout, and can quickly analyze the affected signals and risks under single or superimposed faults and output them explicitly. This study can provide guidance for related maintenance operations of nuclear power plants, or provide reference input for DCS configuration design or function optimization.