Abstract: The gas-liquid-solid three-phase flow of deep-sea hydrates is one of the main factors that induce the failure of mining riser, and a comprehensive understanding of its flow characteristics can effectively improve the safety of mining riser. Based on this, a horizontal wellbore tubing gas-liquid-solid three-phase flow simulation test rig for deep-sea hydrates was developed using analogous principles. This rig enables multiphase flow simulation under varying particle sizes, flow velocities, and phase ratios. Employing a controlled variable method, the effects of different parameters on flow patterns and particle/bubble motion behavior within both vertical and horizontal sections were systematically investigated. The experimental results show that when the gas-liquid-solid ratio is different, the axial velocity of particles decreases with the increase of gas phase ratio in both vertical and horizontal sections, while the axial velocity and radial velocity of bubbles in the vertical section fluctuate greatly when the gas phase content is high. When the particle size is different, the radial velocity variation of particles in the vertical and horizontal sections is larger, and the axial velocity variation is smoother compared to the radial velocity. The radial velocity variation of bubbles is most significant in the vertical section, and more stable in other sections. When the flow velocity is different, whether it is vertical or horizontal, axial velocity or radial velocity, particles and bubbles tend to stabilize at lower flow velocities. The research results can effectively guide the optimization of commercial exploitation parameters for deep-sea hydrates. At the same time, due to the typical gas liquid solid three-phase flow phenomenon in deepwater gas field sand production, low-temperature hydrate production at the seabed mudline, and transmission of fracturing fluid containing low-density proppants, the research results also lay an experimental foundation for the selection of parameters for the above three on-site operating conditions.