Welding　arc　spectral　information　is　a　rising　welding　information　source.　In　some　occasion,　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　arc　spectral　information　of　the　anthor　are　discussed　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　examples,　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　potentialities.　These　content　will　play　an　important　role　in　applying　and　spreading　welding　arc　spectral　information　technology.