Abstract: The Euler-Lagrange coupling scheme based on the continuous and discrete theories has been becoming increasingly popular in numerical analysis of fluid-particle interaction. In this study, by introducing the modified Gaussian weighting function, a new arbitrary resolved-unresolved CFD-DEM coupling method (ARU CFD-DEM) is proposed based on the authors’ previous developed semi-resolved coupling approach by combing the fully-resolved and un-resolved coupling methods. This ARU CFD-DEM method is powerful to relieve the overload in computation due to refining the flow field around the coarse particles in the fully-resolving method. At the same time, it is also able to solve the difficulty in computing the local averaging variables when fine particles with large diameter exist in fluid grids. By doing so, the ARU CFD-DEM is able to simulate the fluid-particle interaction in sand mass which contains a wide range of particle diameters. By comparing with the results of upward seepage flow tests in sand, the accuracy and effectiveness of ARU CFD-DEM model is verified. Furthermore, the hydraulic gradient-flow velocity relationship and soil deformation-flow velocity relationship in the upward seepage flow are analyzed on the particle-scale by the ARU CFD-DEM. The proposed ARU CFD-DEM model can provide a new tool for investigating the fluid-particle interaction in the seepage flow in geotechnical engineering.