Abstract: The friction and wear test of AISI 1045 steel disc sliding against copper pin was carried out on a pin on disc test rig. The copper wear debris was collected in order to count the number of wear particles and analyze the fractal behavior of the particle accumulation. The results indicate that the accumulation of wear particles in the friction and wear process shows a strong bi fractal behavior. There exists difference in the fractal dimensions of the accumulation of small particles and large particles. Moreover, a fractal turning point was observed on the particle size coordinate, which distinguishes the accumulation of small particles and the accumulation of large particles. The position of the fractal turning point is related to the wear condition between the copper pin and steel disc. This could be informative and helpful to the identification of the friction and wear states.