Objective To explore the brain magnetic resonance imaging (MRI) in the evaluation of cognitive dysfunction in patients with OSAHS. Methods Seventy-five patients with OSAHS in radiology were retrospectively analyzed. According to AHI they were divided into the mild OSAHS group, the moderate OSAHS group and the severe OSAHS group, with each group twenty-five patients. Twenty-five patients from one health medical center were taken as the control group. Hippocampal atrophy scores, PVH score, MMSE score, MoCA score in defferent groups was compared and the correlation was analyzed. Results The hippocampal atrophy scores, PVH score in the severe OSAHS group was higher than that in the moderate OSAHS group ,the mild OSAHS group and the control group. The MMSE score, MoCA score in the severe OSAHS group was below than that in the moderate OSAHS group, the mild OSAHS group and the control group. Hippocampal volume contraction, PVH was negatively correlated with MMSE score. Hippocampal volume contraction was negatively correlated with MoCA score, attention, language. PVH was negatively correlated with MoCA score and delayed memory. Conclusions Hippocampal atrophy and focal high signal area around lateral ventricle test from craniocerebral MRI results for cognitive function in patients with OSAHS has certain diagnostic value and deserves further research.