In order to evaluate the impact of ambient conditions on the performance of indirect dry cooling system quantitatively, an analytical model was established which combined the numerical simulation of thermo-flow performance of natural draft dry cooling tower and the thermodynamic analysis of water steam system in a 660 MW thermal power generating unit. The model was verified by experimental results and practical operating data, respectively. Temperature and flow fields of cooling air, as well as the back pressure of turbine were obtained under various natural crosswind and ambient temperature conditions. Standard coal consumption rates were acquired accordingly. The results indicated that the back pressure and standard coal consumption rate increased with the ambient temperature and wind speed. The most additional 27.72 g/kWh of standard coal consumption rate can be caused by the natural crosswind and high ambient temperature for the investigated power generating unit. A sensitivity analysis was conducted and the results showed that the value of the standardized coefficients for natural crosswind speed and ambient temperature were 0.446 and 0.888, respectively. Therefore, though the natural crosswind could deteriorate the flow field of ambient air, the ambient temperature had a greater impact on the standard coal consumption rate. (C) 2018 Elsevier Ltd. All rights reserved.