Welding arc spectral information is a rising welding information source.In some occa- sion,it can reflect many physical phenomena of welding process and solve many problems that cannot be done with arc electric information,acoustic information and other arc information.It is of important significance in developing automatic control technique of welding process and other similar process.Many years study work on welding are spectral information of thc anthor are dis- cussed from three aspects of theory,method and application.Basic theory,view and testing methods of welding arc spectral information has been put forward.In application aspects,many applied ex- amples,for example,monitoring of harmful gases in arc(such as hydrogen and nitrogen)with the method of welding arc spectral information;welding arc spectral imaging of the welding pool which is used in automatic seam tracking;controlling of welding droplet transfer with welding arc spectral information and so on,are introduced.Especially,the successful application in real time controlling of welding droplet transfer in pulsed GMAW is introduced too.These application examples show that the welding arc spectral information has great applied significance and development potentiali- ties.These content will play an important role in applying and spreading welding arc spectral infor- mation technology. Welding arc spectral information is a rising welding information source. In some occa- sion, it can reflect many physical phenomena of welding process and solve many problems that can not be done with arc electric information, acoustic information and other arc information. It is is important significance in developing automatic control technique of welding process and other similar process. Many years study work on welding are spectral information of thc anthor are dis- cussed from three aspects of theory, method and application.Basic theory, view and testing methods of welding arc spectral information has been put forward. In application aspects, many applied ex-amples, for example, monitoring of harmful gases in arc (such as hydrogen and nitrogen) with the method of welding arc spectral information; welding arc spectral imaging of the welding pool which is used in automatic seam tracking; controlling of welding droplet transfer with welding arc spectral information and so on, are introduced. Especia lly, the successful application in real time controlling of welding droplet transfer in pulsed GMAW is incorporated too. these application examples show that the welding arc spectral information has great applied significance and development potentiali- ties. the content will play an important role in applying and spreading welding arc spectral infor- mation technology.