Abstract:  Experiments are carried out to study the fire trace identification of wire insulation ash section by SEM microscopic morphology analysis. The residues are made，such as the fire residue of short circuit caused by long term overload，fire residue of instantaneous short circuit， residue of short circuit caused by fire etc. The production method of residue sample for SEM is developed，and the samples are made. The micro characteristics of the samples is observed and summarized，to identify the primary and secondary short-circuit burn mark as well as the fire mark. This method expands the acquisition path of the material used for fire cause identification，is complements to molten bead identification，improves the evidence chain，thus has significant application value. 

Key words:  SEM analysis, electrical fire, insulation layer, section, fire evidence identification