The invention discloses a method for preparing 
chondroitin sulfate. The method comprises the following steps: adding water to immerse 
cartilage, adjusting the pH value to be 8-9 with alkali, and carrying out heat preservation at 55-60 DEG for 4-6 hours; adding 2709 
alkaline protease, stirring for 6-8 hours, heating until boiling, and filtering to obtain 
chondroitin sulfate liquid; adding 
sodium chloride to the 
chondroitin sulfate liquid, adding ethyl 
alcohol which is 2-3 times of volume of the liquid, standing for 6 hours, and filtering to obtain 
chondroitin sulfate sediments; adding water to the 
chondroitin sulfate sediments for dissolving, simultaneously adding 
sodium chloride to water, and adjusting pH value to be 10-12; adding 
hydrogen peroxide which is 1%-3% of weight of the liquid, oxidizing for 6 hours, and filtering to obtain filtrate; adjusting the pH value of the 
chondroitin sulfate filtrate to 5-6, adding ethyl 
alcohol which is 4-6 times of volume of the filtrate, and participating for the second time, so as to obtain chondroitin sulfate sediments; pouring the chondroitin sulfate sediments into a 
dewatering tank with an emulsifier; pumping ethyl 
alcohol which is 3-5 times of volume of the chondroitin sulfate sediments into the 
dewatering tank, carrying out suction 
filtration, collecting sediments, and 
drying to obtain a chondroitin sulfate product. The chondroitin sulfate obtained by the method is loose in texture, small in particles, easy to dewater and dry, low in 
energy consumption, very low in 
organic solvent residue and short in 
production cycle.