The invention discloses a wear-resisting alloy steel with high boron, high chrome and low carbon and a preparation method thereof, which comprises the following chemical constituents in weight percent: 0.1-0.5% of C, 3-26% of Cr, 0.5-1.2% of Si, 0.5-1.5% of Mn, 0.3-2.8% of B, 0.3-2.6% of Cu, 0.2-0.6% of Ti, 0.02-0.15% of Ca, 0.03-0.25% of Ce, 0.02-0.18% of N, 0.05-0.3% of Nb, 0.04-0.09% of Al, 0.02-0.15% of Mg, 0.04-0.13% of K, less than 0.03% of S, less than 0.04% of P and the balance Fe and unavoidable impurity elements. The method comprises the following steps: melting steel scrap and chromium iron in an electric furnace; adding copper plates, ferrosilicon, ferromanganese into the melted steel scrap and chromium iron, heating the melt to 1560-1620 DEG C after the constituents are adjusted to be qualified in stokehold; adding calcium-silicon alloy and aluminium deoxidation into the melt; and then adding ferrotitanium and ferroboron in sequence, melting and discharging; roasting the compound inoculant composed of granular rare earth magnesium alloy with the diameter being less than 12mm and cerium metal, Si3N4, VN, Nb and K; placing the roasted compound inoculant at the bottom ofa steel ladle; carrying out modification and inoculation processes on the smelted liquid steel by pour-over method in the steel ladle, wherein, the pouring temperature of the liquid steel is 1400-1450DEG C; heating castings to 920-1150 DEG C and preserving heat for 2-4 hours; and air cooling the castings to room temperature to obtain the alloy steel in the invention. The alloy steel of the invention has the advantages of high strength, rigidity and toughness, good thermal fatigue resistance property, wear resistance, and low manufacture cost.