This paper discusses the significance of state monitoring and fault diagnosis of rotating machinery. A framework is put forward to support each other in four aspects of state monitoring and fault diagnosis: theories and methods, key technologies, systems diagnosis, and applications. An example of the research on the system of state monitoring and fault diagnosis for the ultra-supercritical steam turbine generator is given. Progress in the previously mentioned four aspects is reviewed. Finally, thoughts and suggestions about state monitoring and diagnostic studies of rotating machinery are given.