A novel axial-flow hydrocyclone in the ebullated bed reactor is proposed to solve problems such as low space utilization rate, low operation flexibility and complex device structure. This study presents a numerical and experimental study of the liquid-solid two-phase flow and the performance of the hydrocyclone, with focus on the effects of length h(c), taper angle alpha(c) and diameter D-2 of the vortex finder over a certain range of inlet flow rates. Results show that the influence of D-2 on separation performance is more significant than the influence of either h(c) or alpha(c). Increasing D-2, increasing h(c) or decreasing alpha(c) are all beneficial to improve separation efficiency, and separation performance decreases as inlet flow rate increases. When the dimension and structure of the vortex finder and inlet flow rate change, it is always accompanied by a low-level pressure drop (400 Pa-650 Pa). Considering separation efficiency and pressure drop, a hydrocyclone with a cylindrical vortex finder with h(c) of 335 mm and D-2 of 75 mm is the optimum hydrocyclone. Overall, this study provides guidance for the design of axial-flow hydrocyclones for particle separation in ebullated bed reactors. (C) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.