Coal-fired power plants are one of the main sources of anthropogenic carbon emissions that contribute to climate change, and climate change, in turn, tends to increase power demand and challenge the power supply system. Quantifying the impacts of climate change on coal-fired power plants is critical for developing suitable adaptation strategies and stabilizing energy supply. Using monthly data collected from 461 coal-fired power plants in China during the period from 2012 to 2014, this paper explores the influences of a suite of climatic factors and non-climatic factors on power generation efficiency. Furthermore, we project future consequences of efficiency with various climate change scenarios. We find significant heterogeneities in the impacts of temperatures across different types of power plants. On average, a 1 ℃ increase in monthly temperature is associated with an efficiency reduction of 0.09% and 0.32%, respectively, for electricity-only plants and electricity plus heat plants; this means that China’s northern region—which has more electricity plus heat plants—is more vulnerable to climate change. Finally, future projections suggest that efficiency reductions induced by climate change could lead to substantial power supply declines. Under the RCP2.6, RCP4.5, and RCP8.5 scenarios, the power losses would reach, respectively, 5.16 billion kWh/year, 9.32 billion kWh/year, and 15.77 billion kWh/year, accounting for 4.4%, 8.0%, and 13.5% of the national electricity consumption in 2019.