Abstract: Fire marks of copper wires from simulated fire experiment and fire locales were studied by metallographic and macroscopic analysis. The results showed that in the current national standard-GB 16840.4-1997 “Technical determination methods for electrical fire cause Part 4: Metallographic method”,the descriptions of fire marks feature of copper wires in fire is not accurate. Before melted,the description on copper wires fire marks is correct,namely,the microstructure are all large isometric crystals without empty pores. However,after melted,the microstructure of copper wires are mainly isometric crystals,branch crystals and Cu2O-Cu co-crystallization,and even sometimes,with some empty pores.