Extreme drought events can impact human health, notably triggering epidemics that impose significant global health and economic burdens. Understanding these effects and developing response strategies is crucial. However, there is limited epidemiological evidence on how climate change influenced ancient epidemics before large-scale urbanization and frequent population movements. In this study, we utilized the Reconstructed East Asian Climate Historical Encoded Series (REACHES) climate database and the self-constructed ancient Chinese epidemics database to examine extreme drought events in ancient China from 1784-1787 CE. We analyzed factors like grain prices, population density, and socioeconomic conditions to explore the temporal and spatial mechanism and influence the degree of extreme drought events on epidemics outbreaks. The results show that there is a clear positive link between drought and the spread of epidemics, with a notable one-year lag effect of drought. Drought impacts epidemics directly and indirectly through locust plague, famine, crop failure, and social turmoil, with famine being the most crucial factor. Official disaster management can mitigate epidemics. This study intuitively shows the relationship between extreme drought events and epidemics in ancient China and offering insights into the climate change-epidemic relationship. Placing the conclusions of this paper in a broader context has global implications, providing historical experience for polycrisis and modern challenges.