Pipeline hydraulic transportation is an important way for transporting of solid materials. An LBM-DEM based numerical simulation method is established in Visual Studio platform using Fortran language which can model the hydraulic transportation process of coarse particles in the pipeline. The motion of two-layer and three-layer particle swarms with the same volume in horizontal pipe is simulated by this method. The results show that the bedload motion is the main motion mode of coarse particles in horizontal pipelines, and the action of water flow will cause some particles to saltate. There is a low velocity zone in front of the particle group, and the lower the initial flow velocity and the larger the particle diameter, the more obvious the low velocity zone is. The upper particles of the particle swarm will collapse during the motion, and with the increase of the initial flow velocity of the pipe and the decrease of the particle diameter, the upper particles gradually change from collapsing towards the lower layer to collapsing in front of the particle swarm. The stacking mode has an important effect on the movement of particle swarms in the pipeline. There are some differences between the two-layer particle swarm and the three-layer particle swarm in the characteristics of low velocity zone and the collapse mode of particles. This study can provide some guidance for the development of pipeline hydraulic transportation technology for coarse particles.