An airborne-based Direction-Finding System is developed for the application of ELINT and ES(Electronic Support). The system takes the phase-comparison technology, and has the configuration of multi-based antenna array for the solution of ambiguity due to the increased Direction-Finding resolution. This thesis describes the design of optimized distances among antennas, the electrical characteristics, the method of compensation, the direction-finding accuracy, and et. al. under the condition of the airborne-based environment.