A CFD-PBM (computational fluid dynamics-population balance model) coupling model has been established to study the effects of ice packing factor and flow velocity on the ice volume fraction (IVF) and particle size distribution (PSD) in horizontal straight tubes, followed by an analysis of the transport properties of heterogeneous flow in ice slurry pipes. The results show that the ice content has a significant effect on the ice volume fraction (IVF) and particle size distribution (PSD): the higher the ice content is, the bigger the ice volume fraction (IVF) will be, and the bigger the particle size distribution (PSD) will be as well. The main effect of the flow velocity on the IVF distribution mainly focuses on the regions near the wall of pipes. While the ice volume fraction (IVF) in the mainstream almost remains unchanged, the ice volume fraction (IVF) near the wall region decreases. With the increase of velocity, the size of ice crystals increases, while the increasing rate of ice crystals decreases.