Abstract: The heating mathematical model of flux cored wire extension was founded.The temperature distribution rule of flux cored wire extension was measured and calculated when welding parameters were different.The resistance heat made flux cored wire extension heated and the arc heat made flux cored wire melted and the droplet overheated.The influence of shunting current of the flux powder in flux cored wire and arc heat on the heating mathematical model of flux cored wire extension was little and could be ignored when the diameter of flux cored wire is 1.2mm.The thermal dynamics of flux cored wire was analysed with thermogravimetry analysis(TGA) and differential thermal analysis(DTA).The resistant heat caused the decomposition of fluoride compounds,the loss weight of flux cored wire,the oxidization of the Fe-alloy and increment weight of flux cored wire during heating process.The oxidization of the Fe-alloy caused that the transfer efficiency of alloy element became lower and influenced the chemical composition and mechanical properties of weld metal.