The invention discloses a medium chromium alloy wear-resisting steel ball and a preparation method thereof and relates to the technical field of wear-resisting materials. The chemical components of the medium chromium alloy wear-resisting steel ball comprise, by weight, 1.5-1.9% of C, 0.9-1.2% of Si, 0.7-1.0% of Mn, 5.5-7.0% of Cr, 0.3-0.5% of Mo, 0.08-0.20% of Ti, 0.1-0.2% of Cu, 0.02-0.05% of Nb, 0.06-0.08% of Al, 0.02-0.05% of Hf, 0.05-0.1% of B, 0-0.05% of P, 0-0.04% of S, and the balance Fe and inevitable impurities. The chemical components and contents thereof of the medium chromium alloy wear-resisting steel ball are reasonably optimized, the synergy is enhanced, the strength, hardness and toughness of the medium chromium alloy are improved remarkably, the prepared wear-resisting steel ball is excellent in comprehensive mechanical performance, the good impact energy is achieved while the effect that the high hardness HRC is greater than or equal to 61 is ensured, and wear resistance and corrosion resistance are good.