The invention discloses wind power flange alloy steel and a preparation technology of parts thereof. The alloy steel comprises the following chemical compositions: carbon, silicon, manganese, phosphorus, sulfur, chromium, molybdenum, vanadium, nickel, copper, nitrogen, oxygen, hydrogen, rare earth and the balance of iron and the inevitable impurities. The preparation technology of the alloy steel parts comprises the following steps: pretreating molten iron, smelting in a converter, performing external refining, casting steel ingots, performing flame cleaning, heating, forging, slowly cooling, performing heat treatment, machining, performing flaw detection, inspecting, packaging and warehousing. Compared with the existing alloy steel used in the wind power generation at home and aboard, the alloy steel disclosed by the invention has higher tensile strength, yield strength, elongation after fracture and reduction of area, particularly higher low-temperature impact toughness. The atmosphere corrosion resistance and the sea atmosphere corrosion resistance are increased by two levels.