There is not only a gradient pigmentation change in the surface of Dosidicus gigas's beak,but also a significant gradient change of its mechanical behavior. From the rostrum to the wing,the mechanical strength gradually becomes lower but the toughness becomes higher. In this paper,we determined the difference of Young's modulus in different parts of Dosidicusgigas's beaks(rostrum,lateral wall,wing),the main chemical component and the internal molecular cross-linking was determind. The electronic microscope was used to observe the physical structure of the surface and section of different beak's parts. The reasons for the gradient change of the mechanical strength of keratin were discussed. Studies showed that the anhydrous beak has a high Young's modulus,the modulus is not significantly different from the rostrum to the wing (P>0.01),while the hydrated beak's Young's modulus is significantly reduced,the modulus has a Significant gradient change from the rostrum to the wing (P<0.01). The main chemical composition of the beak contains protein, catechol, chitosan and water. The mechanical strength increases with the increasing protein and catechol. The mechanical strength influnces from the internal molecular cross-linking structure and the microscopic physical structure on the surface and section. The internal molecules include:phthalic acid,ethylimidazole,histidine and tyrosine,which are cross-linked to Dopa-multi-cross linked multimers. According to the physical structure,the layered structure of the stalk of the squid is very significant. The stratification is more obvious in the organism and the mechanical strength is greater.