The invention discloses a plant extract and a method for cross-linking collagen by using the plant extract as a biological cross-linker. The plant extract is an amomum villosum extract, wherein the amomum villosum extract contains polyphenol effective components. The plant extract is prepared through the following steps: firstly, cleaning, drying and crushing amomum villosum; secondly, extracting crushed amomum villosum powder in an extracting solution; thirdly, separating the extracting solution; fourthly, concentrating the extracting solution; fifthly, obtaining a concentrated plant extract solution or dehydrated plant extract powder. The plant extract has the benefits that by using the amomum villosum plant extract as the biological cross-linker, molecular chains of the collagen are cross-linked, the structure of the collagen can be stabilized, and the degradation resistance of the collagen is improved, so that the processing characteristics of a collagen product are improved, the physical properties and the texture characteristics are good, and the application prospect is wide.