Sanding phenomenon is a severe problem in the oil and gas fields found in weak unconsolidated formations. While previous experimental researches mostly studied single-phase fluid flow, it rarely happened in real reservoirs. This study presents a novel approach to investigating sand production mechanism from multiphase fluid production through experiment of large specimen size, and a coupled Computation Fluid Dynamics – Discrete Element Method (CFD-DEM) modelling for two-phase flow. The sand production experiments on a weak artificial sandstone were conducted under one-phase and two-phase flow conditions: water flow in water-saturated and gas flow in water-saturated samples using a customized High-Pressure Consolidation System (HPCS). The coupled CFD-DEM numerical simulations of similar conditions were conducted to capture the salient features of sanding behaviour at micro-levels. The discontinuous nature of sand particles and the bonds between them were modelled using DEM, whereas the continuous fluid flow was described by CFD. The experimental results showed that more sand was produced by the two-phase flow of gas through an initially water-saturated sample as compared to the single-phase water flow. The numerical results on the other hand showed different internal void fraction distributions between the two cases, which led to a faster fluid outflow and a slightly higher sand production for the multiphase flow case. The experimental and numerical results were however limited by the experiment duration and the simulation time of an otherwise on-going sand production process.