To investigate PM2.5 reduction by technical improvement in typical Chinese coal-fired power plants, two units built in different time with different particulate matter (PM) control technologies but with the same coal-fired boiler type were selected to characterize the concentrations of PM2.5 generated and emitted from coal-fired power plants. We found that significant benefit of PM2.5 emission reduction was achieved by technological improvement. Due to the increase in the installed capacity and the application of low NOx burner alone, PM2.5 emission factor without adopting other air pollution control devices decreased from 0.153 kg t-1 (the 100 MW unit) to 0.123 kg t-1 (the 300 MW unit). With the help of an improved electrostatic precipitator (ESP) of which removal efficiency increased from 76.4% to 97.5%, PM2.5 emission factor further decreased from 0.014 kg t-1 (the unit with a normal ESP) to 0.003 kg t-1 (the unit with a cold-side ESP and a wet flue gas desulphurization (WFGD)). However, the application of flue gas denitrification and desulfurization devices may alter PM2.5 compositions and their emissions. For instance, the installation of a WFGD was found to largely increase the emissions of water-soluble ions in PM2.5 (e.g., SO42-, Ca2+, and NH4+).