The conformance testing is the foundation to ensure interoperability between on-line monitoring intelligent electronic devices（IED）for transformation equipment，and has great significance for the development of on-line monitoring IED and popularization of IEC61850in smart substation.By analyzing the basic principle of conformance testing，the conformance testing schemes for on-line monitoring device，comprehensive monitoring unit and substation side monitoring unit are proposed，in order to reduce risks of interoperability failure in on-line monitoring system integration process of substation equipment.The conformance simulation testing system is developed，and the implementation methods of IEC61850object model，abstract communication service interface，manufacturing message specification protocol stack and protocol analyzer have been given.By applying self-developed simulation software tool to comprehensive monitoring unit，substation side monitoring unit and Modbus slave station，the on-line monitoring communication process of capacitive equipment is simulated.Besides，the work flow of conformance testing and analysis results of protocol data unit are given，thus the validity and feasibility of the proposed method are verified.