Tanks are very common on portable nuclear power platforms. The gas–liquid two-phase interface inside them is prone to fluctuations due to vessel motion during normal operation, which causes difficulties and errors in liquid level position measurement and affects the safe operation of the system. In this paper, the problem of liquid level fluctuation in a square tank under marine conditions is investigated by CFD with the aim of improving the accuracy and system reliability of liquid level position measurement. In order to study the characteristics and laws of the liquid level inside the tank under different working conditions, a model of portable power plat-form's square tank was constructed using ANSAYS Fluent, and the motion of the gas–liquid two-phase interface inside the tank was simulated under two working conditions: oscillation and swaying. Based on the above calculation results, different anti-shaking measures are designed in the square tank and the simulation of the gas–liquid two-phase interface is carried out. By com-paring the effects of different anti-sway measures, it provides a reference for liquid level position measurement and anti-sway design under marine condi-tions.