Abstract: Nuclear Instrumentation (Nuclear Control System) can realize the non-contact measurement, and it has the characteristics of high precision, fast reaction, well stability and digital, intelligent, network by adopting the computer technology. Nuclear instrument is more and more widely applied to the online measurement with complex processes and high automation in adverse circumstances in steel manufacturing process. Nuclear instrument is also the indispensable basic instrument in the real time control system used to provide all kind of important measurement data.In this paper, the existing situation, development, technology and economic benefit of nuclear instrumentation application in domestic and overseas steel plant was introduced.