Abstract: The previous research has indicated that the 3DOF-rigid-pendulum composite model holds a significant potential for the application in the field of equivalent modelling of non-linear liquid sloshing dynamics within spacecraft tanks. While this model can accurately describe the non-linear sloshing behavior of liquids under conventional gravitational conditions (Including large-amplitude in-plane/out-of-plane lateral sloshing, rotational sloshing, and liquid vortex), the mechanical equivalence of the model under low-gravity conditions requires a further validation. Consequently, a method for identifying equivalent parameters of the rigid pendulum composite model based on data-driven parameter optimization has been proposed. This method utilizes data from the computational fluid dynamics simulation software FLOW-3D to identify key parameters via a particle swarm optimization (PSO) algorithm. This parameter identification method enables the rapid and accurate determination of the sloshing model's equivalent parameters, yielding highly reliable validation results. Research findings indicate that the damping dissipation effect of the liquid cannot be neglected in low gravity environments even for small-amplitude planar sloshing, and that the 3DOF-rigid-pendulum composite model can respond well to the change trend of the sloshing force in large-amplitude planar sloshing conditions, whether it is a harmonic excitation or a step excitation. At the same time, the equivalent parameters of the existing rigid-pendulum composite model are corrected by using the parameter identification method. In addition, through systematic simulation, this research summarizes the mathematical empirical relationships between the equivalent pendulum length and equivalent mass parameters of the rigid-pendulum composite model and the liquid filling ratio under different gravity conditions, which provides a theoretical basis for the subsequent study of the large-amplitude non-planar sloshing problem of liquids.