In order to promote the low-carbon energy transition and achieve the goal of carbon neutrality, the operation of different power generation modes has been simulated based on real data of a province in China. The carbon emission model of coal-fired power units has been developed. With the lowest operating cost as the optimization objective, the power output characteristics of the units during the dispatch period are obtained, and the emission levels of units of different classes are accounted for. The carbon emissions at different wind and solar power installed capacity have been explored and compared. The results indicate that as the installed capacity of wind power and photovoltaic gradually increases, the carbon emission of coal-fired units decreases significantly, but the peaking capacity declines and the low-load operation time rises. This has led to an increase in carbon emissions per kWh of electricity. On average, for every addition of the initial capacity, total emissions will be reduced by 8.70 Mt. This work is favorable to the planning of the clean and efficient transition for coal-fired power units.