The invention relates to the technical field of alloy steel forging and discloses high-performance alloy steel flanges and forgings and a manufacturing method thereof. Alloy steel comprises the components of, by weight, 0.14%-0.17% of carbon, 0.10%-0.60% of silicon, 0.60%-0.80% of manganese, 0-0.005% of phosphorus, 0-0.003% of sulfur, 1.00%-1.25% of chromium, 0.55%-0.65% of molybdenum, and the balance iron. The forgings produced through the manufacturing process are excellent in performance, the performance index of the forgings far exceeds that of forgings produced through a traditional process, and the defect number and size found in forging nondestructive testing are also far superior to those of the traditional process.