Pack Bay in civil aircraft is located in unpressurized area, which contains high temperature components of ECS(Environmental Control System), such as heat exchanger, compressor and so on. In order to avoid high temperature damage to the structure, cooling method should be applied. In this article, a Pack Bay ventilation geometry model is built according to an existing configuration, and then CFD(Computational Fluid Dynamics ) simulation calculation is taken based on this model. After analyzing the calculation results, drawbacks of this configuration are listed, and recommendations for the future design are proposed.