Based on data from the Chinese Longitudinal Healthy Longevity Survey (CLHLS), this study examines the decline of cognitive functions among the Chinese oldest-old born in 1899-1908, 1909-1918 and 1919-1928 using hierarchical linear model (HLM). As one ages, his/her cognitive functions continuously decrease, and such decrease accelerates before death. There are significant cohort differences in the decline trajectories of cognitive functions among the oldest-old. For the later-born cohorts with longer life expectancy, the decline of cognitive functions is delayed, and they also have better cognitive functions than the earlierborn. However, the later-born cohorts experience longer periods of cognitive impairments before death. Besides, there is strong heterogeneity in older people, and those with better socioeconomic environments, healthier states, and more active behavioral patterns have better cognitive performance.