The dynamical interaction of payload brackets and spacecraft frame structure can observably magnify the responses of payloads. Vibration reduction studies usually focus on component-level payload brackets, but in this research, spacecraft frame structure and payload brackets are considered as a whole system (Spacecraft-Bracket System). A certain spacecraft was modeled with finite element method. With structure parameters extracted from this model, a system-level lumped parameter model was built, and the univariate analysis for structure parameters was done. The results indicate that the lumped parameter model can expose the coupling pattern of payload brackets and spacecraft frame structure clearly, and that the sensitivity for responses of payloads related to frequency parameters of both structures are evidently higher than that related to damp and mass parameters. Consequently, for improving the dynamic environment of payloads, the frequency relationship of payload brackets and spacecraft frame structure should be anatomized in spacecraft structure design stage.