Currently the Chinese government has adopted World Health Organization interim target-1 values as the national ambient air quality standards values. However, the population-based evidence was insufficient, especially for the oldest old (aged 80+). We evaluated the association of fine particulate matters (PM) exposure and incidence of disability in activities of daily living (ADL) in 15 453 oldest old in 886 counties/cities in China from 2002 to 2014 using Cox model with penalized splines and competing risk models to evaluate the linear or non-linear association. After adjusting for potential confounders, a J-shaped association existed between PM exposure with a threshold concentration of 33 μg/m, and incident disability in ADL. Above this threshold, the risk magnitude significantly increased with increase of PM concentrations; compared to 33 μg/m, the hazard ratio ranged from 1.03 (1.00-1.06) at 40 μg/m to 2.25 (1.54-3.29) at 110 μg/m. The risk magnitude was not significantly changed below this threshold. Each 10 μg/m increase in PM exposure corresponded to a 7.7% increase in the risk of disability in ADL (hazard ratio 1.077, 95% CI 1.051-1.104). Men, smokers, and participants with cognitive impairment might be more vulnerable to PM exposure. The study provided limited population-based evidence for the oldest old and detected a threshold of 33 μg/m, and supported that reduction to current World Health Organization interim target-1value (35 μg/m) and Chinese national ambient air quality standards (35 μg/m) or lower may be associated with lower risk of disability in ADL.