The invention discloses a preparation method of active carbon with a high specific surface area made from bamboo wood, and belongs to the technical field of resource comprehensive utilization. The method comprises the steps that the abandoned bamboo wood is cleaned, aired, carbonized, then subjected to furnace cooling, broken into certain granularity, dried, and packaged for use; KOH and a carbonized material are mixed uniformly, put in a ceramic crucible and placed in a microwave device; nitrogen is introduced to a furnace to exhaust air in the furnace; heating with microwaves is performed; in the last few minutes of the heating, CO2 is blown in quickly through a conduit communicated with the bottom of the ceramic crucible, and an ultrasonic generator is started simultaneously; after the heating, water washing with tap water is performed and residual KOH is recovered; washing is performed repeatedly with an appropriate amount of hydrochloric acid; cleansing with the tap water and drying are performed; and the active carbon with the high specific surface area made from the bamboo wood is obtained. The active carbon produced by the method is high in specific surface area, high in adsorption capacity, and lower in ash content, has well-developed pores, and can be applied in the medical fields of blood purification, dialysate regeneration and the like after appropriate disinfection and refining.