In response to the poor dispersibility of microcrystalline graphite （MG） as a rubber reinforcing agent， this paper selected 25% ethanol solution with similar surface tension to graphene as the ball milling solvent， and prepared MG ultrafine powder with a median particle size of 1.209 μm through ball milling method. By partially replacing carbon black （CB） as a reinforcing agent for natural rubber （NR）， NR/CB/MG composites with better mechanical properties were obtained. The dispersion of MG and CB in the NR matrix was characterized using field emission scanning electron microscopy （SEM）， and the effects of MG particle size and substitution amount on the properties of NR/CB/MG composites were studied. The results indicate that an appropriate amount of MG can promote the dispersion of CB in the NR matrix and shorten the positive vulcanization time of NR/CB/MG composites； The finer the particle size of MG， the better the mechanical properties of NR/CB/MG composites. Compared with NR/CB composites， its tensile strength， tear strength， 100% elongation stress， and 300% elongation stress are increased by 6.3%， 7.5%， 8.4%， and 6.4%， respectively. The fatigue temperature is risen and the permanent deformation rate is decreased by 2.5% and 44.7%， respectively.