The thermal stability of Cu-14Fe and Cu-14Fe-0.07Ag in situ composites is investigated.The evolution of Fe filaments in two composites is analyzed detailedly by annealing at high temperature.The results indicate that the Cu-14Fe in situ composite exhibits two kinds of evolution of Fe filament,the longitudinal splitting of Fe filaments at low temperature(below 600 ℃) and spheroidization of Fe filaments at high temperature(above 600 ℃).With the addition of trace Ag,the longitudinal splitting of Fe filaments at low temperature is accelerated,while spheroidization of Fe filaments at high temperature inhibited.The microstructure evolution procedure of Cu-14Fe without and with trace Ag has been modeled.This work would promote the understanding of the microstructure evolution of Cu-Fe in situ composite.