The invention relates to high-hardness high-carbon medium-chromium wear-resistant cast iron and a preparation method thereof. According to the technical solution, the high-hardness high-carbon medium-chromium wear-resistant cast iron comprises the following chemical components of, in percentage by weight, 3.61wt%-3.99wt% of C, 12.11wt%-14.99wt% of Cr, 0.51wt%-0.79wt% of Si, 0.61wt%-0.89wt% of Mn,1.71wt%-1.99wt% of Mo, 0.31wt%-0.39wt% of B, 0.51wt%- 0.89wt% of Zr, less than or equal to 0.049wt% of P, less than or equal to 0.049wt% of S, the balance Fe and the inevitable impurities, wherein Cr / C is greater than or equal to 3.35 and less than or equal to 3.99, and B / Mo is greater than or equal to 0.15 and less than or equal to 0.23, burdening is conducted according to the chemical componentsand the contents thereof, smelting, pouring, air-cooling to room temperature, and polishing are conducted; and heating is conducted to 850-1050 DEG C, the temperature is kept for 1-3 hours, quenchinginto oil is conducted, and cooling is conducted to the room temperature to obtain the high-hardness high-carbon medium-chromium wear-resistant cast iron. The high-hardness high-carbon medium-chromiumwear-resistant cast iron and the preparation method thereof have the characteristics of low production cost, simple preparation method and short production period, and a prepared product has good toughness and hardness is significantly improved.