The present invention provides a collagen preparation method, which is characterized by comprising: grease removing, wherein washed and crushed animal cartilage tissue is soaked with hot water; high temperature aging, wherein the grease-removing animal cartilage tissue is subjected to thermal insulation for 1-2 h at a temperature of 70-90 DEG C; enzymolysis, the upper layer aqueous solution obtained after the high temperature aging is removed, an enzyme with the optimal pH value of 7-9 is added to the lower layer mixture, hydrolyzing is performed for 2-5 h at a temperature of 40-68 DEG C, and a weight ratio of the lower layer mixture to the enzyme is 1:0.01-0.1; and impurity removing, wherein the product obtained after the enzymolysis contacts active white clay or a mixture of active white clay and a flocculant. According to the present invention, the collagen preparation method has the mild preparation conditions, avoids the strong acid and strong alkali conditions, and can reduce the danger in the industrial production; and the collagen prepared by using the method has the good color, the good odor and the good translucency due to the removal of the grease and other impurities, and further has the high chondroitin sulfate content and the low heavy metal content.