The dynamic characteristics and liquid sloshing of a circular tank are analysed using ADINA software through seismic response analyses. The maximum sloshing wave height for the circular tank under unidirectional horizontal seismic action is developed. The calculation method involves three parameters such as tank radius, seismic coefficient and dynamic coefficient. The dynamic coefficient of liquid sloshing is determined corresponding to the long-period seismic design β spectrum with a 5% damping ratio using basic sloshing period. The established method can guide the seismic design of liquid-containing structures. The established method of calculating sloshing wave height is compared with those in the American code.