The microstructure of the interface in a Gr f /Al composite after exposure at high temperature was investigated. The graphite fiber reinforced aluminum matrix composite was prepared by the pressure infiltration method. After being heat treated at 550 ° C, 600 ° C and 640 ° C for different times, the microstructure of the interface in the composite was studied by using transmission electron microscopy (TEM). Furthermore, the content of Al 4 C 3 in the interface was examined using X-ray diffraction (XRD). The results showed that not only the micro morphology but also the content of Al 4 C 3 in the interface varied with the increase in temperature. When the composite was heat treated at 550 ° C and 600 ° C, Al 4 C 3 with a big length-todiameter ratio was observed in the interface, while Al 4 C 3 with a small length-to-diameter ratio was found when the heat treatment temperature was 640 ° C. With the increase in the time, the content of Al 4 C 3 in the interface increased rapidly when the composite was heat treated at 640 ° C. Based on the dynamic calculation, the interface reaction diffusion rate constant of the Gr f /Al composite increases rapidly when the temperature is higher than 600 ° C.