To enhance the isolation performance of the current three-parameter isolators, a prototype of broadband fluid damping strut has been designed. The damping strut features several frequency selective valves to adjust its damping characteristics at the low-frequency range, and a machined spring with a clearance element to act as a secondary stiffness. A dynamic mathematical model and a simulation model of a vibration isolation system using the designed fluid damping strut for a spacecraft control moment gyroscope have been established, followed simulation results indicate that compared to current three-parameter dampers the designed damping strut has achieved adaptive outer characteristics of high damping in the low-frequency range and low damping in the high-frequency range, it has obtained a significant suppressive effect on low-frequency vibrations, especially those near the resonance peak, its statistical vibration isolation effect is also better than that of the current dampers in the mid and high frequency bands, thus, the designed fluid damping strut has obtained excellent vibration isolation characteristics in a broad frequency band.