The quality of the airborne power system is crucial to the safe flight of the aircraft and the normal work of the avionics. In the test flight of electronic testing machines, avionics are in different working conditions, which may affect the quality of the airborne power system. Therefore, it is needed to continuously monitor the airborne power system in flight test, and evaluate the quality of power supply. Aiming at this problem, an on-line monitoring system for airborne power system is developed to realize the on-line monitoring of the multi-working characteristic parameters of 115V/400Hz three-phase AC and 28V DC power continuously. The system is based on high-performance dedicated computer and high-speed synchronous data acquisition cards. It can collect voltage and current of airborne power system in real-time, and use related data processing algorithm to perform real-time operation for multi-working characteristic parameters, and display and store these parameters, and the voltage and current of the abnormal working point are recorded for the later analysis. The system has been tested on a certain electronic test machine and the monitoring results are real-time and accurate. It is of great significance for improving reliability and fault location of airborne power system.