Recently, there is a rising interest in smart grid operating system which manages various types of distributed generation, smart meters, and electric vehicles with power grid. Considering the features of smart grid environment, the interoperability should be one of the important factors to build smart grid environment successfully. To secure interoperability, smart grid operating system should conform to some standards in terms of the data representation and communication. CIM and OPC-UA are the international standards widely used in smart grid domain for enabling interoperability. They provide common information model and the unified architecture for communicating between each systems or applications. In this paper, we illustrate a smart grid operating system that we have developed to secure interoperability between not only applications but also numerous legacy systems(applications) by implementing CIM based information model and OPC-UA based communication interface services.