The Chinese government launched pilot programs for a long-term care insurance system in response to the ongoing increase in the aging population. This study uses the difference-in-differences (DID) model to analyze the impact of long-term care insurance on older adults' mental health based on China Health and Retirement Longitudinal Study (CHARLS) four-period panel data from 2011 to 2018. This study found that long-term care insurance reduced Center for Epidemiological Studies Depression Scale (CES-D) scores among older adults by 1.059 points. Moreover, there was an improvement of 0.181 and 0.870 points in mental status and scenario memory scores, respectively. The impact of the long-term care insurance pilot program on improving the mental health of older adults was more pronounced, especially for those with chronic diseases or disabilities as well as those living in rural and western regions. This study also revealed that long-term care insurance enhances mental health by reducing medical expenses and increasing daily companionship and social interaction. Therefore, a pilot study of long-term care insurance showed a significant improvement in the mental health of older adults. To provide a comprehensive care service system for older adults, the government should expand the scope of the pilot program and increase the accessibility of mental health services for older adults.