Abstract: According to the environment where short-circuit of copper wire stay, the effect of smoke particle concentration on such structural characteristics as grain boundaries and pores as shown in the trace of fused copper wire was investigated. The results showed that with the increasing smoke particle concentration the grain boundaries in the trace turn to discontinuity from continuity and the number and area fraction of pores both increase gradually. It implies that there is a correspondence between the area fraction of pores and smoke particle concentration, i.e. if the concentration remains unchanged, the highly viscous smoke particles affect greater the formation of pores in the trace than lowly viscous smoke particles.