Middleware is a kind of fundamental software that boomed in 1990s with the rapid development of computer networks. Its main function is to effectively support the development, deployment, operation and management of the network application software systems. With a new connotation, the network computing middleware has encountered a breakthrough of information networks technology and service-oriented software engineering. The former part of this paper, which starts with the network computing environment, gives a comprehensive interpretation on the basic concepts and main technologies of basic middleware, application integration middleware and domain application framework; the second half focuses on hot research topics such as cloud computing, Internet of things, and indicates a number of concerned research directions as well as several challenges and key technologies that need deep exploration from the point view of middleware.