Abstract: To ensure the reliability of equiments mounted in the avionics pods, an environmental control system (ECS) should be equipped in the pod independently. There are two difficulties in designing pod ECS: one is that the aircraft has no enough electrical power to drive the pod ECS; another is that some elements and devices can't suffer higher temperature, which requires a good environmental condition. This paper introduces a new ram air driven ECS for the avionics pods, which adopts the design concept of cool thermal storage for saving energy. The system operates on a reverse bootstrap air cycle and with a regenerative heat exchanger as well as an intelligent control subsystem. To overcome the difficulty of low ram air pressure head, by use of aerodynamic theory, the total pressure recovery σ of the ram air inlet is raised and the differential pressure between the inlet and outlet air of the ECS is increased, therefore, the greater expansion ratio ε of the cooling turbine is acquired. Test results demonstrate that the designed system has good performance.