Objective To analyze the correlation between brain atrophy and cognitive impairment in patients with Alzheimer.Methods 45 cases of Alzheimer in recent years in our hospital were selected as the observation group, and 45 patients without Alzheimer in the same period in our hospital as control group.The relationship between brain atrophy and cognitive impairment in patients with Alzheimer was analyzed.Results The width of temporal and anterior horn of lateral ventricle, three ventricle, quadrigeminal and the average width of lateral fissure, the body and occipital lateral cerebral ventricle and sulci in the observation group were significantly bigger than that in the control group.The memory, orientation, problem solving ability, social function, family life, the degree of self-care ability impairment of the observation group were significantly higher than that of the control group (P<0.05).Conclusion Brain atrophy is a specific marker of Alzheimer, which may lead to cognitive impairment.