Abstract: Substation configuration description（SCD）file is important data for equipment operation,routine operation and maintenance,project management in smart substation.In view of the engineering application problems brought about by the high degree of coupling in the SCD model,the necessity and urgency of the decoupling technology about the SCD model is expounded.For the smart substation expansion project,the scheme of SCD bay physical decoupling is analyzed,and the bay modeling method based on the system specification description（SSD）model is put forward,which makes secondary devices grouped into the bay.The SCD model is decomposed into a number of bay files mainly by physical decoupling.And the unrelated bay,the correlation bay and the new bay are defined for the smart substation expansion project scenario.By means of physical isolation,automatic analysis of the relationship between the bay based on the SSD model,hierarchical signature comparison configuration modification,the unrelated bay is isolated and modification errors are avoided.The area of the configuration,debugging and testing,etc,is reduced for the smart substation expansion project.For engineering application requirements,the configuration process of SCD bay decoupling is given for the smart substation expansion project.Current main problems demanding prompt solu-tion for SCD bay decoupling are analyzed.