Abstract: In order to obtain the effect and electrical injury of the flames and radiant heat on the wires and connecting parts in actual fire scene,a T3 copper plate 4 mm thick was welded by TIG at different temperatures.Through the mechanical and electronic properties and microstructure analysis of welded joints and a comparison of the crystallization and heat treatment theory of metal with fire mechanism,the effects of temperature on the microstructures and properties of copper welded joints were investigated.The results show that the hardness will be slightly higher due to enhanced annealing when the fire temperature is low,which does not affect by fire.But when the temperature is above 650 ℃,the hardness significantly declines,which causes the seriousness damage;electrical resistivity has little changes.The microstructures of welded joint is coarse grains of α-Cu and crystal within the celluliform metastructure generated.With increasing temperature,the grain growth and the number of sub-structure decrease and diffuse.