The invention provides alloy steel for an energy storage flywheel casting and a casting method of the energy storage flywheel casting. The alloy steel comprises the following components by weight: 0.55%-0.60% of carbon, 0.23%-0.33% of silicon, 0.42%-0.52% of manganese, 1.55%-1.65% of chromium, 3.95%-4.05% of nickel, 0.31%-0.41% of molybdenum, less than 0.015% of phosphor, less than 0.015% of sulfur and the balance of iron and inevitable impurities. The casting method of the energy storage flywheel casting comprises the following steps: making wood dies; making cores by using alkali phenolic resin sand; carrying out filling shrink on a contact site of a flywheel rim and a wheel arm by using a blind riser; carrying out mould closing casting; insulating the casting in a sandbox, and opening the sandbox to clear the sand; and carrying out gas cutting on casting heads, so as to finish casting of the energy storage flywheel casting. The alloy steel has high strength and can satisfy performance requirements of wheel hubs. The casting method has advantages of simple process, convenient production and high efficiency.