Solar aided (coal fired) power generation (SAPG) is the synergy of solar thermal energy and fossil power plant technologies by using solar thermal energy to replace extraction steam to preheat feed water. SAPG combines environmental benefits of the former and large capacity, high efficiency and reliability of the latter. However, there are no appropriate criteria for evaluating the thermal performance of the system now. In this paper, a new evaluation method of SAPG system is proposed based on the exergy analysis and the characteristics of exergy flows crossing the boundary of the system. In the established evaluation method, a new ideal cycle is constructed in the perspective of external heat sources, and the difference of solar proportion among the exergy input, work output and exergy output in the same subsystem is considered. With the evaluation method, the contribution proportion of solar energy in a SAPG system can be determined. To illustrate applications of the new method, a parabolic trough solar field aided 600 MW coal-fired power generation system is discussed as a case study. (C) 2016 Elsevier Ltd. All rights reserved.