A new fast online analysis system development project, sponsored by the State Grid of China, was started in 2006. The primary goal of the project was set to reduce the online analysis overall round-trip time, from data acquisition to complete the analysis, from the current proximate 10 minutes to less than 60 seconds. The project development work has been completed at the end of 2018. A pilot new online analysis system has been deployed and running in a provincial dispatching center in China. The preliminary testing data indicates that the new online analysis system can achieve sub-second response speed. Digital Twin (DT) has been in the Gartner�s Top 10 Strategic Technology Trends list every year since 2017. In the project development, an Online Analysis Digital Twin (OADT) has been implemented. In this presentation, the DT concept will be introduced in the context of application to power grid online analysis. A high-level overview of the project and some of the preliminary performance testing results will be presented. The overview will include the project high-level solution architecture, the DT concept used in framing the solution architecture, the OADT implementation to support the solution architecture realization, and the pilot online analysis system implementation details.