The invention discloses a method for extracting huperzine A from a serrate clubmoss herb. The method comprises the following steps: (1) pre-treatment; (2) ultrasonic countercurrent extraction: carrying out ultrasonic countercurrent extraction on the serrate clubmoss herb and filtering to obtain leach liquor; (3) membrane separation and purification: centrifuging, and carrying out ultrafiltration and nanofiltration on the leach liquor to obtain trapped fluid; (4) concentration, namely concentrating the trapped fluid into paste; (5) acid dissolution, dissolving the paste by using acid liquid, filtering, and adjusting pH to alkalinity; (6) extraction: extracting by using chloroform and collecting extract liquor; (7) concentration: concentrating the extract liquor to obtain dry powder; (8) crystallization and recrystallization: dissolving to obtain the dry powder, crystallizing and recrystallizing to obtain white crystals; and (9) drying, namely drying the white crystal to obtain a huperzine A product. According to the method disclosed by the invention, the purity of the huperzine A extracted from the serrate clubmoss herb is greater than or equal to 99%, the product yield is greater than or equal to 0.026%, the final yield is 50-55%, and the yield, yield coefficient and purity of huperzine A is high, the extraction time is short, and the cost is low; therefore, the method for extracting huperzine A from a serrate clubmoss herb is suitable for industrial production.