Abstract: For obtaining the vibration characteristic of liquid-structure interaction system on rectangular liquid-storage structure, mode test for liquid-structure interaction system of steeliness rectangular liquid-storage structure was presented. Former four nature modes of vibration and corresponding natural frequency of liquid-structure interaction system with no liquid and liquid, with different roof thickness and the different liquid densities were obtained, and the influences of the storing liquid, the relative thickness of roof and the density of liquid on the natural frequency of liquid-structure interaction system were analyzed. The results showed that storing liquid would lower the natural frequency of liquid-storage structure, increase of roof thickness would increase the natural frequency, and increase of liquid density would have little effect on the natural frequency. The experiment provides basis for subsequent study and application of liquid-structure interaction system of rectangular liquid-storage structure.