Antheraea pernyi (A. pernyi) silk is produced and used by “wild” silkworms to construct a cocoon, but the primary structure of its protein is rather similar to that of spider major ampullate silk used to build web and dragline. Studies on this specific silk may provide valuable knowledge about the structure-property relationship for the whole animal silk family. In this work, A. pernyi silk fibers with few macroscale defects are obtained by forcibly reeling, and are investigated in detail. It is found that such silk fibers display breaking stress and toughness of the same magnitude as spider major ampullate silks and forcibly reeled mulberry silk. The other mechanical properties, such as elasticity, supercontraction, and the effect of water on modulus are between those of spider major ampullate silks and mulberry silk. Therefore, an interpretation of the connection between the primary structures of silk proteins and the mechanical properties of silks is proposed here based on the ordered fraction, which in turn is determined by both the protein sequence and spinning process of the silk.