The experiment showed that HYD extract can down-regulate PEN-2 expression and γ-secretase activity through inhibiting the CREB binding site activation of PEN-2 gene promoter, intervene in APP metabolic pathways, reduce the production of Aβ1-40 and Aβ1-42, restrain the formation of senile plaques, reduce the loss of neurons, improve memory, and then inhibit AD occurring and developing. The gene discussed is APP; the disease is Alzheimer disease.