Abstract: As a main energy source in China, coal-fired power’s objective and accurate carbon emission accounting are vital for national carbon emission reduction policies making, al ocation of carbon emission quotas, and efficient operation of carbon trading mechanism. In this paper, an on-line carbon emission monitoring system for thermal power units has been developed and successful y applied to a 660MW unit. The results show that the CO₂ emission concentration of the unit is 9.32 ～ 15.03%, while the measured carbon emission per minute, per hour and per day are 5 ～ 8 t, 265 ～ 475 t and 8 099 ～ 12121 t, respectively, carbon emissions related with unit power generation. The carbon emission intensity is 655 ～ 1377 g/（k W·h）, which is negatively correlated with unit load with a fit coefficient R~2=0.1512. The relative errors between the on-line monitoring method and the manual comparison method are + 3.9% and-2.9%, respectively, with the loads of 350 MW and 600 MW. The deviation rate between on-line monitoring method and emission factor accounting method is 11.7% ～ 16.8%, indicating that the former has good quality. As the deviation between the two methods is directly affected by the coal-burning compliance and the representativeness of the measuring points. It is suggested to increase the sites of sampling and put the sites on the chimneys to improve the accuracy. The development of this system and the analysis of carbon emission characteristics of units wil further promote the application of carbon emission on-line monitoring technology in thermal power enterprises, and provide reference for low-carbon dispatching of power grid. Moreover, it can also support monitoring, management, and trading of carbon emissions.