Abstract: To address the issues of sand sedimentation and sand dune accumulation during proppant transport by slick water system in horizontal wells, and to clarify the unclear mechanisms of sand transport and migration, this study aims to reveal the primary controlling factors and their influencing patterns on proppant deposition and sand dune evolution under various operating conditions. Utilizing a self-developed in-house horizontal pipe sand-carrying flow loop experimental system, visualization experiments under different operating conditions were conducted. Experiments were designed with varying slick water viscosities (5 and 20 mPa·s), proppant sizes (20/40 mesh and 40/70 mesh), proppant concentrations (10% and 20%), and flow rates (0.15 to 0.63 m³/min) to investigate the coupled effects of sedimentation and resuspension on sand dune evolution. Results indicate that increasing flow rate and viscosity significantly enhances the fluid’s proppant-carrying capacity and reduces sedimentation, whereas higher proppant concentration and larger particle size intensify particle settling, increasing sand dune height and delaying equilibrium. The dune evolution exhibits a dynamic balance characterized by "front advancement and height accumulation." The relative influence of controlling factors is in descending order of proppant concentration ＞ flow rate ＞ viscosity ＞ particle size. Based on experimental data, the critical sand sedimentation flow rate and severe sand-plugging flow rate were quantified, providing fundamental insights into proppant transport and deposition behavior in horizontal wells and laying the groundwork for subsequent predictive modeling.