Abstract: ObjectiveTo investigate the subjective memory impairment ( SMI ) in prodromal stage of amnestic mild cognitive impairment( aMCI) and the clinical value of P300 of event-related potentials in early diagnosis and evaluation of Alzheimer's disease.Methods: The cognitive function of the SMI group，aMCI group and control group ( 20 cases each group ) were assessed using multidimensional neuropsychological testing， the event-related potentials of three groups were detected.The change characteristics and differences of P300 between three groups were analysed.Results: The AVMT-delay memory recall，AVMT － immediate memory and CDT in SMI group scores were higher than the aMCI group and the control group( P 0.05 － P 0.01) ，but there was no significant difference between the aMCI group and the control group( P 0.05) ; the level of VFT in SMI and aMCI group were significantly higher than the control group ( P 0.01) ， the VFT in SMI group and the aMCI group showed no statistical difference ( P 0.05) .The connection testing，DS and CFT copying score test in the three groups had no statistical difference ( P 0.05) . Conclusions: The neurophysiological testing has important clinical value in early diagnosis of aMCI and SMI in prodromal stage，but P300 testing has no value for SMI and aMCI clinical diagnosis.