Abstract: The present invention provides a walnut oligopeptide powder, a preparation method and application thereof. The oligopeptide powder has a peptide content of 80 wt % or higher, in which 95% or more of the peptides have a molecular weight of less than 1,500 Da. The method includes extracting walnut proteins using a highly efficient countercurrent extraction process, and subjecting the extract to filtration, enzymolysis, purification with a microfiltration membrane and an ultrafiltration membrane, concentrating, and spray drying to obtain the oligopeptide powder. The oligopeptide powder has an anti-oxidant activity and provides a protective effect for a neuron, and thus can ameliorate or treat memory deterioration and relieve fatigue.