Aiming at the fluid-structure interaction analysis of irregularly shaped liquid storage tanks in nuclear power engineering, a high-precision additional mass distribution model was established based on the acoustic-structural coupling method (CAS), which improved the calculation efficiency of structural seismic analysis. The hydrodynamic pressure of the liquid on the vessel wall is equivalent to the inertial force generated by the motion of the mass point along the vessel wall, and the fluid-structure coupling analysis of the structural system is decoupled. Firstly, based on the CAS method, the dynamic analysis of the irregular liquid storage container under sinusoidal excitation is conducted. By setting the boundary conditions of the free liquid surface, the pulse component of the hydrodynamic pressure is peeled off, and then the additional mass components of each node are obtained. The additional mass is then applied to the overall structure, and the seismic dynamic analysis includes the influence of the hydrodynamic pressure on the structure. Taking the rectangular water tank as an example, the proposed model is compared with the Housner distributed mass model, which verifies the correctness of the proposed model. Based on the proposed model, an annular water tank in nuclear power engineering is analysed. The results show that the basal reaction time history calculated by the distributed mass model is in good agreement with that calculated by the CAS method; The hydrodynamic pressure of liquid on the wall is mainly impulse hydrodynamic pressure; The impulse mass is about 50% of water body, and the overall effect is basically the same as that of the original liquid sloshing model. The research results can provide a new technical means for fluid-structure interaction analysis of seismic design of nuclear power engineering.