<p>Patients with hypertension commonly experience metabolic dysfunction and cognitive decline. Previous studies have shown that sedentary behavior can affect metabolism. The weight-adjusted waist circumference index (WWI) has become a new indicator of obesity. This study examines the association between sedentary time and hypertension combined with cognitive decline (HCD), with a focus on assessing the mediating role of WWI. A total of 6098 hypertensive patients from May 2022 to July 2024 were included in this study from the hypertension follow-up system. Various statistical techniques such as logistic regression, subgroup analysis, smoothed curve fitting, and causal mediation analysis were used in the study to analyze the information collected from hypertensive patients. In completely adjusted models, there was a noteworthy statistically positive relationship between sedentary time and HCD with an odds ratio (OR) of 3.50 and a 95% confidence interval (CI) of (2.37, 5.16). The causal mediation analysis showed that the relationship between sedentary time and HCD was partially influenced by the mediating effect of WWI with a mediation ratio of 3.6%. Based on this study, sedentary time was significantly and positively associated with the prevalence of HCD, with WWI playing a mediating role. This finding provides a new perspective on the prevention and management of HCD.</p>