Abstract: The power bus ripple of spacecraft reflects the spacecraft's health condition and can be used to predict its future trend. This paper provides a design of a power bus ripple measuring system based on the PXI frame, and a certain spacecraft is tested in an uninterrupted test for the power bus safety to give the dynamic characteristics of the power bus. The methodology can be used in the model design and test analysis. This system solves the problems, such as the low security and the small data capacity in the past years based merely on oscilloscope or scope meter to test the ripple, and it might play a key role in the electrical test of spacecraft.