Alzheimer's disease (AD) is the most common form of neurodegenerative disorders leading to dementia. Currently, there has been no effective drugs targeting this disease. Dysbiosis of the gut microbiota is considered to be associated with AD, and probiotic supplementation may positively affect cognitive function. However, there are few studies involving the relationship between intestinal microorganism and amnestic mild cognitive impairment (aMCI). In this project, taking the method of random, double blindness and control, the probiotic supplemented group with aMCI will take certain Bifidobacterium for a certain time. After that, the investigators aim to investigate the improvement of cognitive function and changes of intestinal microbial flora diversity via combining neuropsychological tests and 16S recombinant deoxyribonucleic acid (rDNA) high-throughput sequencing technique. Furthermore, based on the multi-modal neuroimaging techniques, the regulatory mechanism of intestinal microorganism in intervening aMCI will be revealed from the perspective of brain networks. In conclusion, these results are beneficial for understanding the therapeutic effect of gut microbiota as a non-drug treatment for early AD and further elucidating the potential brain mechanism, which are of great values in solving scientific and clinical practice issues.