As the collagen protein market increasingly grows, it becomes a priority to explore a economic, stable, and environmentally-friendly extraction method to realize the high-value transformation of pigskin. In this paper, the structure of collagen protein is introduced first. Then five methods, which extract collagen protein from pigskin or a kind of leather industry waste-chrome shavings, are reviewed. These methods include the salting out method, alkali method, acid method, enzyme method and hybrid method. They are contrasted in several ways, and thus provide evidence for better extracting collagen protein.