The authors make a brief introduction to application and development of water jet technology in hot rolling line in iron and steel works,introduce the principles of high-pressure water jet descaling technology and controlled cooling technology as well as roller cleaning machine,which were used widely in hot rolling line in iron and steel works,describe the functions and selecting principles of main components of high-pressure water jet descaling system and controlled cooling system as well as roller cleaning machine,predict the future of R & D and application of water jet technology in iron and steel industry.