To extract the electrophysiology characteristic index for early diagnosis of vascular dementia(VD)

the event related potential(ERP)of persons with different cognitive faculty was analyzed. Vascular demented patients were compared with healthy elderly control group and youth group

and VD patients also were divided in two groups

mild and serious VD patients according to mini mental scale examination results. The visual oddball paradigm was used and ERP signals were analyzed by approximate entropy(ApEn). The results show that ApEns of serious VD patients do not change obviously and remain stably. On the contrary

the ApEns of other groups decrease as stimulus appears and increase as stimulus over.The ApEn of mild VD patient gets higher than that of healthy elderly control and youth

and the difference degree becomes the largest during stimulus reaction. ApEn analysis demonstrates the brain activity change of subjects with different cognitive faculty clearly during cognitive work

and the reflect degree of cognitive ability of brain

which provides a novel method for early diagnosis and classification of VD.