The tribological behavior of poly(tetrafluoroethylene) composites filled with various metallic particles was investigated under the extreme friction conditions of a heavy load and reciprocation with a small amplitude. Two obviously distinct friction stages corresponding to the contact conditions were found. The phenomena of the accumulation of fillers on the contact surface and extrusion wear of the poly(tetrafluoroethylene) matrix were also observed. Based on the experimental results, the actions of metallic fillers on the transfer film formation were analyzed. It was noted that the transfer and accumulation of fillers could actually be considered to be an assimilating process of the friction pairs. Accordingly, the physical model of the transfer film formation process was described and some suggestions on the mechanism of load-supporting actions of hard fillers were also proposed.