Abstract: The physical and mathematical model of the 3D airflow and heat transfer was set up for the helicopter nacelle.Unstructured grids and grid adaptation was applied to the region discretization,taking the characteristic of nacelle configuration and air flow into consideration.For five cooling system design configurations,numerical simulation of the 3D airflow and temperature field was carried out using the standard k-ε turbulent model and finite volume method.The influence of inlet and outlet size and their distribution on velocity field and temperature field was analyzed.The results show that the inlet located in front and the outlet located aft of the nacelle is of benefit to the airflow flow and heat transfer.Air eddy was found in nacelle,and the temperature in the front part of the nacelle was higher than the rear part.