Abrasive wear is a typical failure mode of various rubber and plastic mechanical sealing equipment. This study researched effect of the abrasive size on the tribological behavior of O-type rubber sealing pairs, analyzed the time-variant characteristics of friction coefficient under water-lubricated conditions with different abrasive sizes and discussed its wear morphology, particle movement characteristics and failure mechanisms within different operation stages. The result demonstrated that the particle size had a significant influence on the tribological properties of the rubber/metal seal pairs. There were two critical particle size values (approximately 12.5 μm and 75 μm) affecting the friction coefficient and the failure mechanism. When the size was larger than the critical value (75 μm), the particles were impossible to pass through the sealing interface, only a few particles can be embedded on both sides of the contact zone of the friction pair producing a deep furrow on metal surface. When the size was between the two critical values, a “particle-embedded band” on both sides of the contact pair can be observed, and single particle or agglomerated particles are embedded in the rubber. The rubber had a good bearing capacity, and a low friction coefficient with reduced wear of the rubber, although it abraded the counterpart metal. When the size was less than the critical value of approximately 12.5 μm, the particles can pass through the friction interface freely, which polished the surface of the counterpart metal and accelerated the erosion wear of the rubber. The worn surface of rubber presented the alternated “ridge-valley” feature, and this should be avoided.