The top-level design of China's basic medical security system is gradually improving, but the reimbursement level of basic medical insurance is still limited for some high medical expenses. The supplementary medical insurance, which is linked with the basic medical insurance and is available to all the participants of the basic medical insurance, will serve as a compensation means to spread risks in a wider range to meet the medical needs of the people. Therefore, the impact of the supplementary medical insurance on the utilization of medical services for middle-aged and elderly people was studied.Data from the 2018 China Health and Aging Tracking Survey (CHARLS) were used to construct a two-part model for analysis. The result is that supplementary medical insurance increases the likelihood of medical checkups, outpatient visits, and hospitalizations for middle-aged and older adults, while reducing their expenditures on outpatient . The government should encourage residents to buy supplementary medical insurance, so as to solve the problem that basic medical insurance can't meet patients' demand for medical services, and relevant suggestions are put forward for the development of supplementary medical insurance.