Abstract: Indirect air-cooling system’s characteristics will receive a greater impact on factors such as ambient temperature. Therefore, this paper selected two different forms of technology-optimized indirect air-cooling tower systems, namely, the three-tower in one type and the main and main-auxiliary combined type, to study the operating characteristics of the unit under the change of ambient temperature in the summer by CFD(Computational Fluid Dynamics). The results show that: with the increase of ambient temperature, the heat exchange situation of both sides of the two types of indirect air-cooling systems deteriorates most seriously. When the ambient temperature reaches 40 ℃ and 39 ℃, the outlet temperature of circulating water reaches 68.1 ℃ and 62.5 ℃, respectively. Anyway, in the main and auxiliary systems, the influence of the rising ambient temperature on the heat exchange of the main engine is only 54.9% of that of the auxiliary area, which shows that it has a greater influence on the heat exchange of auxiliary engines. But the heat transfer uniformity of each fan section of the mainframe is not affected. The increase in ambient temperature will have a great impact on the system performance, the higher the ambient temperature, the higher the operating back pressure of the system. In high-temperature conditions, it is necessary to apply cooling measures to the unit for normal operation. In addition, the main engine back pressure of the main and auxiliary systems is not affected by the auxiliary engines during the temperature increase.