Understanding the depression status of middle?aged and elderly patients with chronic diseases and its relationship with the utilization of medical services is of great practical significance to optimize the allocation of medical resources. Based on CHARLS2015， using Logistic regression， we explored the influence of depression on the utilization of medical services of chronically ill people from two dimensions of outpatient and inpatient services， and tried to explain the influence mechanism by taking self?reported health as the mediating variable. The conclusions include：①Depression significantly increased the probability of medical service utilization in middle-aged and elderly people with chronic diseases. The probability of outpatient and inpatient service utilization increased by 8.4 percentage points and 4.8 percentage points， respectively. ②Self?rated health played a partial mediating role， and the mediating effect affecting outpatient and inpatient service utilization accounted for 46.02% and 63.92% of the total effect， respectively. Depression can directly predict the medical service utilization in middle?aged and elderly people with chronic diseases or indirectly predict the medical service utilization via self?rated health as the mediating variable. It is suggested to increase the intervention for depression of patients with chronic diseases， pay attention to the cognitive ability of self?rated health status of middle?aged and elderly people， and improve the level of health cognition， so as to promote the rational and effective allocation of medical service resources.