Coal-fired power generation in China is facing huge challenges due to its high share in the total electricity generation and its environmental problems. A solar-aided coal-fired power generation (SACPG) system, based on the integration of solar thermal energy into a conventional coal-fired power system, is an effective way to utilize solar energy and reduce coal consumption. The reasonable allocation of output electricity to solar energy and coal in a SACPG system and the evaluation of its CO2 emission reductions can help to acquire subsidies or financial support granted to renewable electricity and CO2 emission reductions. A methodology is proposed from the view of the technical characteristics of a SACPG system and the government regulation. The coal-to-electricity efficiency of the baseline unit or the coal-fired power system in a SACPG system is the key factor in the methodology, and it can be calculated on the basis of the norm of energy consumption of coal-fired power units in China. Then, the allocation of the output electricity to solar energy and coal can be calculated, and so can the CO2 emission reductions by the solar-coal hybrid system. Taking a 600 MW SACPG system as an example, the methodology is further illustrated. The methodology can guarantee that the calculation of output electricity allocation in a SACPG system and the calculation of its CO2 emission reductions are accurate, conservative and transparent for its subsidies or financial support.