Sloshing wave height of vertical storage tanks under earthquake action is one of the main criteria for tank design, and the wave height formulas of seismic codes for storage tanks at home and abroad are based on the theoretical formulas of first-order sloshing. Whether the wave surface vibration of vertical storage tanks under real seismic action involves the participation of higher order array is a problem needed to determine. In this study, the sloshing response of 10,000 square vertical storage tanks under earthquake action was analyzed by finite element software ADINA. The test results show that the sloshing wave height of vertical storage tanks is linearly related to the peak acceleration of input ground motion, and the ratio of the two excitation wave heights to the response peak acceleration keeps the same, and the influence of different liquid storage ratio on the sloshing wave height and the first-order sloshing period is small. In addition,the location of the radial extreme point of sloshing wave height remains different under different earthquake motions. The closer the extreme point was to the core of the tank, the richer the mode of sloshing participation is, the more obvious the mode superposition is. It shows that the sloshing of liquid storage under earthquake is the result of multi-order mode superposition.