Objective：This study aims to evaluate the construct validity of the Alzheimer’s disease assessment scale - cognitive subscale（ADAS-Cog）among Chinese older people population. Methods：A total of 628 normal controls，572 patients with mild cognitive impairment（MCI） and 76 patients with Alzheimer’s disease（AD） were collected to assess the construct validity of ADAS-Cog. Results：In general，the correlation coefficients between the scale and the total scores of ADAS-Cog in AD and MCI groups were between 0.51-0.83 and 0.27-0.69. The construct validity of AD group was better than that of MCI group，but all of them were not good enough. In the factor analysis of the AD group，two factors were analyzed：memory（including word recall and word recognition）and cognitive function（all other scales），which accounted for 63.23% of total variance. Four factors were extracted from the MCI group：memory（including word recall and word recognition），language（including recall of test instructions，spoken language ability，word-finding difficulty and comprehension of spoken language），ideation（including naming objects and fingers and ideational praxis）and commands，with a cumulative variance interpretation rate of 68.02%. Conclusion：This study confirmed that ADAS-Cog had good item correlation and structural validity in evaluating AD population，but was poor in MCI population.