The invention discloses a method for extracting 
carrageenan, which comprises the following steps: washing a 
raw material with water, performing combined alkali treatment on the 
raw material, wherein the concentration of alkali is decreased gradually, washing the 
raw material to enable the pH to be 7-8; carrying out composite 
enzyme treatment, removing 
heavy metals by using a 
metal chelating agent, boiling 
carrageenan, filtering coarsely, filtering finely, reducing temperature, gelling, 
dewatering, 
cutting into strips, 
drying, crushing and screening so as to obtain the 
carrageenan. According to the invention, a 
mixed solution of NaOH, KOH and LCI with gradually 
decreased concentration in three grades is adopted in an alkali treatment process, the loss of carrageenan is reduced effectively while the alkali 
treatment time is reduced; 
cellulase and 
protease combined treatment is adopted, and the yield of the carrageenan is improved while the high 
gel strength of the carrageenan is ensured; 
ethylene diamine tetraacetic acid and nopotassium 
phosphate are adopted for further treatment for the raw material, and the 
heavy metals in the raw materials are removed effectively. The 
gel strength of the carrageenan prepared by the method is greater than or equal to 2139.2 g / cm<2>, the extraction rate is greater than or equal to 23.9 percent, Pb is less than or equal to 2.5 mg / kg, As is less than or equal to 1.0 mg / kg, Hg is less than or equal to 0.5 mg / kg, and the Cd is less than or equal to 1.0 mg / kg.