China’s coal-fired power generation has accounted for a large proportion of the power supply for a long time and the resulting environmental pollution and waste of resources have hindered the sustainable development of the power industry. To solve this problem, this study combines the concept of natural and managerial disposability with the non-concave meta-frontier method to determine the unified efficiency measurement of 251 coal-fired power plants in China from 2012 to 2014 and to investigate the sources of inefficiency in different areas. The results show that although the unified efficiency of China’s coal-fired power plants improved significantly during 2012–2014, much room for improvement remains in terms of power generation and environmental performance. Due to the advanced technology of coal-fired power plants, the eastern area has the highest unified efficiency in terms of natural and managerial disposability. The western region has the lowest operational performance and the northeast region has the lowest environmental performance. The decomposition of the sources of inefficiency indicates that the inefficiency of coal-fired power plants in eastern China is mainly caused by management factors, whereas the inefficiency in northeastern China is due to a lag in technology. In the central and western areas, technical inefficiency and management inefficiency both account for a considerable proportion in their sources of inefficiency. Therefore, these regions need to improve both the management (e.g., reasonable allocation of utilization hours) and technology (e.g., clean coal technology) aspects to improve the unified performance of coal-fired power plants.