Based on the functions and performance analysis of networked virtual instrument (NVI) system, this paper design and implementation the software system of a NVI with the .NET platform. And carry out an in-depth analysis of the software system, especially the key techniques including databases, DataSocket and multithreading. The system uses ASP.NET, C# for development server pages, the instrument operation instructions embedded in Web pages using ActiveX techniques. Using VC to development VI server applications, and through DataSocket to transfer testing data. The testing results show that the software system is operating well, the NVI system achieves a convenient user and testing resource management, and making the system more users to share testing equipment to improve efficiency.