A numerical analysis and experimental validation of sloshing phenomenon in three-dimensional square tank with varying resonant frequency and amplitude of excitation is carried out in this study. Numerical simulations using fluid-structure interaction (FSI) was carried out and validated with experimental result. Square tank is numerically simulated with 50, 100 and 200 mm of water height excited at its 25%, 50%, 75% and 100% of resonance frequencies. Numerical study has been extended to study sloshing phenomenon at different ratio of resonance frequencies to that of varying amplitudes 30, 40 and 60 mm. Pressure of liquid in container during excitation were recorded at specific intervals of time and analysed. Increase in amplitude and frequency of excitation is directly proportional to pressure of liquid in tank. Sudden impulse of velocity of tank has an impact over the pressure built inside tank. The sloshing phenomenon in vertical and horizontal baffle configuration is also examined. © 2020 Informa UK Limited, trading as Taylor & Francis Group.