The invention relates to a method for extracting hirudin. The method comprises the following steps: washing and freezing Hirudo and grinding as a whole into a slurry, heating the Hirudo to 60-80 DEG C and keeping the temperature for 2-3min, regulating the pH value to 4-4.4, then cooling to 25-30 DEG C, adding NaCO3 with the mass concentration of 10%, regulating the pH value to 6-7, adding purified water and purifying for 3 times, carrying out net collection on all leach liquor, centrifugalizing with a tube centrifuge, dialyzing the mother liquor with dialysis membrane for 36h, replacing the dialysis membrane once every 12h, preparing the crude product of hirudin by using a freeze drying method, and finally preparing the refined product of hirudin through freeze drying. The extraction method is reasonable in process, convenient to operate and practical. The finished product of hirudin has the characteristics of good quality stability and high yield. The yield of the hirudin extracted by the method of the invention is up to more than 99%.