Abstract: The microstructure feature of the copper wire and the melted bead and trace in several condations of simulated test were analyzed in this paper. The results reveal that the microstructure of the single wide copper wire melted bead and trace in the fire burned and second short circuit is different from the first short circuit and over load and poor contact. It would provide reference evidence for the fire disaster cause appraisal. But for the copper formed of more thin wire, there are all columnar crystal and equiaxle crystal and small recrystal pellet in the microstructure of copper wire melted bead and trace in the fire burned and second short circuit and in the first short circuit and over load and poor contact. So it wouldn't provide reference evidence for the fire disaster cause appraisal.