The invention relates to a method for purifying collagen derived from pelodiscus sinensis. The method is characterized by comprising the steps of soaking, fat removal and enzymolysis; in an enzymolysis process, carinas of the pelodiscus sinensis, of which impurities are removed, are put into acetic acid with the concentration of 0.5mol/L, wherein the ratio of the carinas to the acetic acid is 1:25, pepsase enzymatic hydrolysate is added for enzymolysis treatment, and extraction is carried out at 4-10 DEG C for 24-48 h, so that a pelodiscus sinensis carina collagen coarse extracting solution is obtained; in a salting-out purification process, the coarse extracting solution is dissolved into a Tris-HCL buffer solution containing NaCl, the mixed solution is centrifuged to obtain supernatant, NaCl is added into the supernatant, salting-out is carried out, centrifugation is carried out again, and precipitates and the supernatant are respectively collected; and precipitates are dissolved into acetic acid with the concentration of 0.5 mol/L, and freeze-drying is carried out after dialysis, so that the pelodiscus sinensis collagen freeze-dried product is obtained. Compared with the prior art, the method provided by the invention has the advantages that collagen extracted through enzymolysis is purified through a salting-out purification method, so that no environment pollution is realized, the extraction efficiency is high and the obtained product has good biological characteristics.