The characteristic of constant power loads is one of the typical characteristics of more electric aircraft power supply system. Combining of aircraft power supply system with constant power load. In order to get the stability condition of the power system with constant power load, as the research object, DC regulated power supply system in airborne is simplified equivalent circuit. The equivalent mathematical model is developed for the constant power loads, and analyzes its theories. According the Routh criterion of automatic control principle, the conclusion which increasing motor compensation capacitance can improve the stability of the power system with constant power load is obtained. Through the simulation and experiments can prove the accuracy of these conditions. The results can be used in the design and optimization of the circuit.