Abstract: In order to investigate the mechanism for Cu-FeS composite (the mass fraction for reinforced FeS phase is 15%) thermal conductivity and the internal structure, the thermal conductivity for composite and reinforced phase were calculated by the molecular dynamics simulation model of FeS particle in the copper matrix and model of interface thermal barrier resistance. The calculated results show that： the structure of FeS changes in 600K and 900K; the interface thermal barrier tends to a constant when the size of particle is over 100nm. The difference between test and simulation for thermal conductivity is caused by the ignoring of imperfection and destruction of interface during heating, matrix defection, and the different particle sizes. The HasselmanJohnson model is suitable for the thermal conductivity prediction.