Abstract: The infrared radiation monitoring system is systematically used in the present study to investigate the characteristics of infrared radiation,influences of the heat input on the relative intensities of the infrared radiation and the weld shaping during laser welding of TA15.It is found that the relative intensities of the signal can be obviously divided into three phases for the whole weld seam:the starting state of welding,the quasi-stable state,and the arc suppressing of welding.When the heat input increases(laser power keeps constant with welding speed decreasing),the weld pool width increases,and the relative intensity of infrared radiation signal increases accordingly.Such findings indicate that molten pool and relative intensities of infrared radiation share the same rules of variation.These changes on the area of molten pool can be monitored exactly,which reflect the stability of welding process by observing the infrared radiation signal.