α-L-fucosidase (AFU) is an acid hydrolase that exists in organisms and widely exists in tissues, cells, blood and body fluids. AFU is involved in the metabolism of glycoproteins, glycolipids and oligosaccharides, and plays a key role in cell differentiation, apoptosis, inflammation and host-pathogen interaction. AFU catalyzes the hydrolysis of the colorless substrate nitrophenyl-α-L-fucoside to produce yellow nitrophenol with a significant absorption peak at 405 nm, and its absorbance is positively correlated with the content of nitrophenol. The activity of AFU can be calculated by measuring the change of absorbance value at 405 nm.