Gravel-packed completion has been widely recognized as the optimal solution for sand control, but due to the limitation of the simulation method, the gravel phase is approximated as the liquid phase, and the numerical simulation is carried out by the Eulerian-Eulerian method, which is more efficient in calculation but reduces the calculation accuracy and is not realistic enough, leading to the optimisation of some of the construction parameters in the field is still problematic. In this study, a numerical model of gravel filling in horizontal wells is constructed based on the coupled DEM-CFD method which can achieve accurate particle tracking, and the influence of gravel density, viscosity, gravel concentration and sand-carrying liquid discharge on the gravel filling degree is investigated, and the degree of densification is proposed as a new evaluation index, and the results of the study can provide theoretical guidance for the construction in the field.