Abstract: The coupling analysis of Computational Fluid Dynamics (CFD) and Discrete Element Method (DEM) has become an important approach to reveal the mesoscale mechanisms of soil-water coupling. In this context, the volume fractions of the particulate phase and the fluid phase are key parameters in determining the interaction between the two phases in the unresolved coupling analysis of CFD-DEM, significantly affecting the computational efficiency and accuracy of the results. For soils with wide particle size distribution, the particle sizes vary significantly, making it difficult to account for both large and small particles during the calculation of the volume fractions, resulting in unstable computation and low accuracy. This study proposes an improved distributed point algorithm for volume fraction calculation. By allocating the volume of effective distributed points within the particle influence radius and transforming the search on the fluid grid to the search of the distributed points, the algorithm significantly expands the applicable range of the ratio of fluid grid size L to particle diameter D. Additionally, by employing the particle mirroring method and the satellite point method, the algorithm achieves compensation for the volume of large particles and precise capture of the volume of small particles. Numerical experiments on particle static arrangement are conducted. After calibrating the algorithm parameters, the coupling accuracy and efficiency advantages of the distributed point algorithm under different types of grid conditions are verified. Through numerical experiments on turbid water infiltration, the accuracy of the distributed point algorithm in calculating particle volume when both D∼L and D≪L coexist is further validated. The numerical experiments demonstrate that the improved distributed point algorithm has broad application prospects in large-scale fluid-solid coupling calculations for soils of wide particle size distribution.