Alzheimers's disease (AD) is a continuous pathological physiology process, including pre- MCI(mild cognitive impairment, MCI), MCI and dementia. For the irreversible of the clinical course of AD, finding early and treat right in the stage of preMCI or MCI are very important for slowing down or even reverse the procession of AD. Research shows that type 2 diabetes mellitus (T2DM ) is an independent risk factor for MCI and AD . This manuscript is a brief review of current concepts in the mechanisms potentially linking T2DM with cognitive impairment.