AC drive system with common DC-bus is widely used in industry process, however, because of inductance in rectifier and negative resistance characteristic of inverter-motor system, DC-bus fluctuation often appears. With small signal method and power-fed AC drive test-bed, this paper studies stability of AC drive system with common DC-bus. First, structure of AC drive system with common DC-bus and power-fed test-bed are introduced, and its small signal mathematic model is derived. Then, stability of test-bed is studied from the point of DC-link stability, and system parameter and operation point effect on stability is also discussed. Beyond that, system stability area is compared with ordinary AC drive system. The conclusion shows that common DC-bus system has a priority than ordinary AC drive system without power-fed structure in the view of DC-bus stability. Experiment results validate above analysis conclusions. What’s more, the conclusion provides an advice for drive system parameter choice.