The invention discloses an IGCC power station peak regulating device achieving energy storage through an air separation system and a method. The device comprises a gasification furnace, a synthesis gas purification unit, a gas turbine power generation system, a waste heat boiler system and a steam turbine power generation system; oxygen needed by the gasification furnace is supplied by the air separation system; the air separation system comprises an air cooling and compressing system which supplies cooling air to a rectifying tower and can achieve variable frequency regulation, air in the rectifying tower is separated into nitrogen and oxygen, nitrogen and oxygen are stored in a liquid nitrogen storage tank and a liquid oxygen storage tank respectively, the liquid oxygen storage tank is connected with an oxygen heater through a liquid oxygen pump and a cold box, and high-pressure oxygen coming out from the oxygen heater is delivered to the gasification furnace. According to the device and method, the defects that an IGCC power generation system is low in load varying speed and poor in power grid peak regulating capacity are overcome, the capability of quickly regulating the IGCC output power is achieved through the storage capacity of the air separation system, and the whole-plant output power can be increased and decreased by within 20% most quickly in a short time.