Abstract Background Subtle cognitive decline (SCD) is considered the early stage of Alzheimer's disease (AD) and is of great clinical significance for the prevention and treatment of AD. The ankle‐brachial index (ABI) has been reported to be associated with cognitive impairment; however, there are few studies on the relationship between ABI and SCD. Methods From August 2019 to April 2021, subjects were recruited to participate in a cognitive function test at the Shanghai Sixth People's Hospital. Based on the test results, 217 patients with SCD were selected as the experimental group and 259 patients with normal cognitive function were selected as the control group. The data of the two groups were compared, and the correlation between the ABI and cognitive decline was analyzed. Results There were significant differences in age, sex, smoking status, hypertension, diabetes, triglycerides, serum creatinine, and ABI ( p < .05)between the two groups. Logistic regression analysis showed that age, hypertension, diabetes, and ABI influenced cognitive decline( p < .05). After correcting for other factors, ABI was independently related to cognitive decline. Pearson's correlation analysis showed that a low ABI (<0.9) had a significant effect on memory and visual space of the cognitive domain ( p < . 05). Conclusions ABI is significantly associated with SCD and may be a critical tool to predict early cognitive decline.