A method for manufacturing a gas mask canister using a HEPA filter media having plastic separating plates inserted into between HEPA filter media at certain intervals. The HEPA filter, impregnated activated carbon, and a pre-filter are accommodated within a cylinder. The cylinder is inserted into a canister having an upper portion and a lower portion detachably coupled together. The impregnated activated carbon, the plastic separating plates and the casing of the canister can be reused, and the rest of elements are burned. A vinyl coating sheet is peeled off from the canister after each use. An indexing tab for recording the number of times of peeling is attached on each of vinyl coated sheets, so that the number of uses can be known.