A new way of energy saving for existing coal-fired power plant that uses low-or medium-temperature solar energy as assistant heat source was proposed to generate ‘green’ electricity. This paper has built the mathematical models of the solar-aided power generation system focusing on the NZK600-16.7/538/538 units. Based on the combination of the first and second law of thermodynamics, the thermodynamic performance of different components of the integrated system was evaluated under the changing operating condition aiming at different substitution options for turbine bleed streams. It has been found that the efficiency of the solar heat to electricity enhances with the increase of the load and the replaced extraction level. Additionally, when the second extraction is replaced, the effect is the best, which makes the power output increase around 6.13% or the coal consumption rate decrease 13.14 g/(kW · h) under 100%THA load and CO2 emission reduce about 32.76 g/(kW · h), while the energy and exergy efficiencies of the integrated system are 39.35% and 39.12%, respectively. The results provide not only theory basis and scientific support for the design of solar-aided coal-fired power plants, but also a new way of energy saving and optimization for the units. Copyright © 2014 John Wiley & Sons, Ltd.