Introduction: China has entered an aging society, and achieving successful aging has become a pressing issue for both society and individuals. Health is a crucial prerequisite for successful aging; however, data indicate that the health status of middle-aged and older adults in China is far from optimistic, with approximately 55% experiencing multimorbidity. Existing research has shown that cognitive decline is a critical factor affecting health in older populations. Nevertheless, current studies face two key limitations: First, health assessments predominantly focus on physical function and activity indicators, overlooking multidimensional factors such as chronic diseases. Second, the underlying mechanisms through which cognitive function influences health remain inadequately explored. Objective: To examine the direct and indirect effects of cognitive function on health by measuring multiple health indicators, using depressive symptoms as a mediating variable. Methods: Using data from the China Health and Retirement Longitudinal Study in 2011 (T1), 2015 (T2), and 2020 (T3), this study included 10,855 participants aged 45 and older. Descriptive statistics and cross-lagged models were conducted, with mediation effects tested via Bootstrap. Results: (1) Cognitive function at the prior time point was positively correlated with self-rated health and negatively correlated with the number of chronic diseases at the subsequent time-point, while showing unstable associations with health behaviors; (2) All three cross-lagged models met goodness-of-fit criteria. Cognitive function at T1 negatively predicted depressive symptom at T2; Depressive symptoms at T2 negatively predicted self-rated health and health behaviors at T3, positively predicted number of chronic diseases at T3; (3) Mediation analysis further confirmed that a decline in cognitive function can lead to an increase in depressive symptoms, which in turn result in lower self-rated health, fewer health behaviors, and more chronic diseases. Conclusion: Cognitive function is a risk factor for health in middle-aged and older adults, with depressive symptoms mediating its effect.