Housner's spring-mass model has poor applicability to complex large nuclear power project liquid storage structures. The fluid-solid coupling numerical analysis model based on finite element method is complex with large calculation and storage capacity, which is difficult to meet the requirements of engineering design. Based on the Coupled Acoustic-structure method (CAS), the paper proposed a model accounting for both accuracy and efficiency of the distribution of quality. Through theoretical derivation from CAS calculation results of the wall of dynamic water pressure impulse component, the paper put forward the wall unit position of each node of the distributed pulse formula of added mass, which accurately considers the shape of liquid storage containers in analysis of liquid sloshing. At the same time, the decoupling of fluid-structure coupling analysis is realized, which effectively solves the problem of dynamically analyzing complex large nuclear power project liquid storage structure. Taking rectangular rigid water tank as an example, the proposed model is compared with Housner's distribution model to verify the rationality and reliability of the model. The ground motion analysis of AP1000 containment structure with complex water tank at the top is carried out, and the comparison between the proposed model and the refined fluid-structure coupling model shows that the results of the two models agree well, and the proposed model is simple in pre-processing and has obvious advantages in calculation efficiency. This model can lay a foundation for efficient multi-factor coupling analysis of nuclear power project considering structure-foundation and fluid-structure coupling.