NOVELTY - Extracting-separating huperzine A from Huperzia serrata or its hairy root using supercritical fluid extraction-crystallization technology, comprises e.g. (i) crushing dried H. serrata or hairy root; (ii) performing microwave radiation; (iii) processing supercritical carbon dioxide extraction; (iv) adding the gradient crystalline paste with superfine silica powder, extruding, using e.g. methanol as cosolvent, and performing supercritical gradient extraction and crystallization; (v) carrying out structural identification; and (v) separating compounds, and detecting purity.    USE - The method is useful for extracting-separating huperzine A from H. serrata or its hairy root using supercritical fluid extraction-crystallization technology.    ADVANTAGE - The method: greatly improves the yield; utilizes inexpensive ethanol as a solvent to greatly reduce the production cost; reduces the production cost up to 40%; separates five high-purity alkaloids; utilizes raw materials having huperzine A content of more than 0.0025% with industrial production values to achieve maximum resource utilization; and utilizes carbon dioxide discharged after the supercritical extraction, which is condensed and compressed to enter the first-grade extracting kettle for the next round of extraction with cosolvent ethanol, which saves the carbon dioxide consumption, reduces discharge, and achieves energy-saving and environment-protecting requirements (claimed).    DETAILED DESCRIPTION - Extracting-separating huperzine A from Huperzia serrata or its hairy root using supercritical fluid extraction-crystallization technology, comprises (i) drying higher content H. serrata or hairy root in shadow, crushing into dry powder of 40-100 meshes, and taking 1% hydrochloric acid or 1% tartaric acid, carbon dioxide fluid, ethanol, acetone and carbon tetrachloride, where the mass ratio of carbon dioxide and dry powder alkaloid content is 100-200:1, and the mass ratio of carbon dioxide to ethanol is 100:(2-10); (ii) placing the dry powder of H. serrata plant or its hairy root into an extraction kettle with a microwave device, adding acid for soaking overnight, turning on the microwave for radiating 120-240 seconds (limited to not greater than 60 degrees C of water temperature) with a radiation frequency of 2300-2600 MHz, where the power is 3000-6000 W; (iii) processing supercritical carbon dioxide extraction by filling with ethanol as a cosolvent at 34-60 degrees C for 40-80 minutes under extraction reactor pressure of 15-45 MPa, transferring the extract into a first-grade separator, separating the residue of the paste solution at 30-40 degrees C under the pressure of 15-45 MPa, feeding the paste solution into a secondary grade extraction kettle, proceeding secondary grade extraction at 30-40 degrees C for 1t with the pressure of 15-45 MPa, feeding the secondary grade extract into a second-grade separator, separating out paste, ethanol and carbon dioxide at 30-50 degrees C under 5-15 MPa pressure, condensing and compressing the carbon dioxide to transmit into the first-grade extraction kettle with ethanol for the extraction of the next round, and finishing the circulation for 3-5 hours; (iv) directly adding the gradient crystalline paste in the second grade separator with superfine silica powder, uniformly stirring, extruding through a screen over 100 meshes, uniformly mixing, respectively using methanol, ethanol, acetone, chloroform as the cosolvent at temperatures of 32-38 degrees C, 42-48 degrees C, 52-58 degrees C and 62-68 degrees C with the different pressure of 11-13 MPa, 15-17 MPa, 19-21 MPa and 23-25 MPa respectively, performing supercritical gradient extraction and crystallization, and respectively obtaining five natural alkaloids; (v) carrying out structural identification to the separated compounds using ZF-1 UV analysis instrument (Shanghai Gucun village instrument factory), Tensor 27 type infrared spectrometer (produced by Btaker company), potassium bromide tableting method, VarianMat-711 mass spectrometer, Bmker DRX-500 nuclear magnetic resonance, where tetramethylsilane (TMS) is the internal standard, the unit of chemical shifting value is parts per million, the unit of coupling constant is Hz; and (v) separating compounds using high performance liquid chromatography (HPLC), detecting the purity of the compounds by an area normalization method, where the purity of the separated compounds reaches 99%.