The present invention relates to a S-substituted-2-amino-3-mercaptopropionate derivative, a preparation method and an application thereof. The S-substituted-2-amino-3-mercaptopropionate derivative in the present invention has a structure of a formula (A). The present invention also includes an application of the S-substituted-2-amino-3-mercaptopropionate derivative serving as a medicine for treating and/or preventing neurodegenerative diseases, particularly Alzheimer's disease.