Mild cognitive impairment (MCI) has been conceptualized as a transitional state from normal aging to dementia, who have some cognitive impairment beyond that expected for age and education but of insufficient severity to constitute clinical criteria for dementia. Impairment of episodic memory is the core feature of amnesia mild cognitive impairment (aMCI). Episodic memory consists of the processes of encoding and retrieval, the study focused on the episodic retrieval. In previous event-related potentials (ERP) studies, the older adults demonstrate the positive-going parietal old/new effect and right frontal old/new effect in the process of episodic retrieval. Especially, ERPs from the older adults contained a large left-lateralized negative effect that overshadowed the left positive-going effects evident in the young when the source accuracy did not differ according to age. In the study, we try to figure out the discrepancy of the three retrieval-related ERP old/new effects between aMCI and the older adults when the source memory performance was matches between the two groups by manipulating the number of items per session of study and test. Source memory paradigm was applied in the study, of which the materials we use are picture and the source of the items is the left or right locations. In the condition that the older adults complete 80 items for one time and aMCI for four times, the two groups perform equally. The results showed that, on one hand，the positive-going left parietal and a large left-lateralized negative effect demonstrated in normal control group. On the other hand, the positive parietal old/new effect disappears in aMCI, and the negative effect demonstrated in aMCI is larger and sooner than normal control, which indicated that aMCI is impaired in using conceptual source information for source judgment, instead they have to rely on retrieval visual information to perform the source memory task. Because of the fact that the significant discrepancy of the ERP pattern can be found between the aMCI and normal control when the source memory performances of the two groups were matched，the study provides a more sensitive neuromarker of the early detection of dementia.