Objective To investigate relationship between different degrees of asymptomatic carotid artery stenosis and cognitive impairment. Methods The cognitive function were evaluated with the montreal cognitive assessment scale (MoCA) in 80 patients with asymptomatic carotid artery stenosis and 56 controls, the total MoCA scores and subprojects scores were compared between the patients with different degrees of ACS and controls. Results The total MoCA score, visual space and executive function, attention and delayed recall had significant difference among the mild, moderate, severe ACS patients and control group (all P < 0.05). There was no statistical significance of the total MoCA score and the scores of all subprojects between the patients of mild ACS patients and the control group (all P > 0.05). The total MoCA score and the scores of visual space and executive function , attention and delayed recall in moderate and severe ACS patients were significantly lower than the control group and mild ACS patients (P < 0.05). Furthermore, the severe ACS patients, compared with the moderate ACS patients , performed worse on the cognitive tasks which involved visual space and executive function, attention and delayed recall (P < 0.05). Conclusions Cognitive function is impaired in the patients with moderate and severe ACS,the neuropsychological characteristics are mainly impaired in visual space and executive function, attention and delayed recall.