In order to improve the control level of intelligent substation SCD file, adapt to Condition-Based Maintenance strategy of relay protection based on life cycle management, explore the operation and maintenance technology of intelligent substation relay protection, this paper presents a SCD secondary virtual circuit identification technique based on semantically intensive. According to the semantic strength, tag semantics and structural semantics are identified layer by layer, decouple the SCD file and write it to the XML file in Schema mode. The standardization of secondary virtual circuit of intelligent substation is judged by special software program. Analyzing key problems of online management of SCD of intelligent substation, the consistency with engineering configuration and the evaluation of protection status, deducing the application mode of protection state maintenance strategy. Actual engineering case test certificates that the method can ensure the accuracy of secondary virtual circuit identification, and complete checking secondary virtual circuit of intelligent substation. Relay protection online monitoring device RSS-501 can adapt to current intelligent substation operation and inspection characteristics, and provide technical ideas to solve the problems of difficult relay protection maintenance and insufficient maintenance depth of intelligent substation.