The indirect dry cooling system, consisting mainly of the dry cooling tower and condenser, keeps energy balance under stable state. However dry cooling tower is easily influenced by the variation of ambient condition, like ambient temperature and crosswind, and theses unfavorable effects will affect the operation of the condenser directly and further impact unit efficiency. Therefore it is necessary to study the effects of ambient temperature and crosswind on thermo-flow performance of the tower under energy balance of the indirect dry cooling system. Taking a 600 MW indirect dry cooling system as an example, numerical simulation model of the dry cooling tower and thermal calculation model of the condenser are established respectively. With the method coupling the two models, the pressure, temperature fields and streamlines are presented. The indirect dry cooling system regains equilibrium after ambient condition varies, and parameters of the system under this stable state are obtained. These parameters reflect the effects of ambient conditions on the thermo-flow performance of the tower under energy balance of the system rather than under the condition that the tower is viewed as isolated. When the power unit is steady running with a certain load, outlet water temperature of the tower is approximately linear with ambient temperature, whereas nonlinear with crosswind speed. In addition, the computational models and coupled method mentioned in this paper are proved reliable enough for the performance prediction of the tower under energy balance of the indirect dry cooling system, which is beneficial to the economic and safe operation of the unit. •Simulation model coupling the dry cooling tower and condenser is established.•The coupled method is based on energy balance of the indirect dry cooling system.•Outlet water temperature of the tower is nonlinear with crosswind speed.•Outlet water temperature of the tower is nearly linear with ambient temperature.•The coupled method is reliable for predictions under various working conditions.