Due to the high temperature in the process of coal combustion, some of the Pb-210 and Po-210 in coal is released with other air pollutants into the environment. In order to evaluate the radiological impact of coal-fired power plants (CFPs) to the surrounding environment, Pb-210, stable Pb and Po-210 from the stacks of five units of CFPs were sampled and measured in China, and stack emissions were calculated using direct measurements of flue gas and comparison of mass between raw materials and solid wastes. According to the measurements in 17 units of CFPs from China, the USA and Slovenia, the proportions of Pb-210 and Po-210 released from CFPs in the total input were 2.1% and 3.7% based on measurement data of flue gas. The emission ratio of stable Pb from CFPs should be correlated to that of Pb-210. The emission ratio of Pb was 1.2%, based on the measurements of flue gas in 60 units of CFPs from China, the USA, Finland and Japan, and 12% based on mass balance in 28 units of CFPs in China; there is a big discrepancy between these results. The factors considered that could have caused this discrepancy were sampling methods (especially for the capture of ultrafine particles), measurement methods, representativity of samples, and the influence of desulphurization and denitrification processes. There is an urgent need to develop novel technologies for the direct measurement of Pb-210 in flue gas and the efficiency calibration of Pb-210 and Po-210 sampling in flue gas.