Considering large optomechanical structures, a fluid damper was designed with high damping and low axial stiffness in the full frequency range to reduce the width of frequency noise. Firstly, the theory of parameter design for a liquid damper was reviewed. Secondly, the characteristics of the fluid damper were verified using the finite element method, in addition to its influence on the entire structure. The simulation results indicated that the use of a liquid damper could effectively increase the structural damping of a spacecraft without affecting its mechanical characteristics. Moreover, it was shown that the line of sight of an optomechanical structure can be improved by more than 50% generally. The test system used to study the characteristics of the design parameters of the dampers was designed as part of this investigation. It was determined that the damping of the liquid damper decreased with an increase in frequency. A coefficient of more than 300 N·s/m was obtained at 300 Hz, while the change of the stiffness with frequency remained approximately the same. These results indicate that the experimental data are consistent with the simulation results, and the design of the stiffness and damping properties of liquid dampers satisfied the requirements. In summary, the effectiveness of liquid dampers on vibration suppression of large optomechanical structures was verified based on simulation and test results.