Supercritical water gasification (SONG) is famous for achieving complete conversion of raw organic matter with the temperature below its ash melting point. Inorganic mineral components associated with raw organic matter will form solid slag particles after the reaction of SCWG is completed. Discharge of the slag particles from reactor is a supercritical water (SCW) transporting particles process under transcritical temperature conditions driven by pressure difference. A comprehensive three-dimensional two-fluid model (TEM) is firstly developed in this study to research the flow dynamics characteristics during the particle transport process. The effect of transport pressure difference (AP) and particle outlet position (All) on particle transport are investigated. Results show that the particles can be transported out the reactor smoothly under the action of AP, and the solid -containing ratio, sr, can reach to 78.27% with AP of 5 MPa and Al! of 55 mm. Large AP can enhance particle transport efficiency, but it may cause fluid overheating in the cooler. When the particle outlet is close to the reactor inlet, a large amount of SCW from reactor inlet will enter the particle outlet, which will decrease the particle transport efficiency. The current model can reasonably clescTibe the flow dynamics characteristics of particle transport process, which may provide theoretical guidance for the design and optimization of slag-discharge system. 2020 Elsevier B.V. All rights reserved.