In order to characterize quantificationally the wear topography of the brazed polycrystalline cBN (PcBN) grains during grinding, the reconstruction model of grain topography is established through the photographs grasped with three-dimensional (3D) optical video microscope. The relationship between 3D fractal dimension and the complicated topography change of the PcBN grains is investigated based on fractal theory. The results obtained show that it is reasonable to calculate 3D fractal dimension according to the protrusion height of the abrasive grain. The fractal dimension of the grain wear topography formed due to microfracture is higher than that formed due to large fracture and attritious wear. The fractal dimension range of the wear topography of the brazed PcBN grains is limited to 2.0325–2.0475 with a concentrated value of 2.04 under the present experimental condition.