Dispersion and natural ventilation of hydrogen leaked at the floor center of a confined space are analytically and numerically studied in this contribution. Two symmetrical openings located atop two opposite walls and several sets of partition boards with varying heights, 0-1.0 m with 0.2 m increment, mounted under the ceiling were designed to examine their effects on ventilation efficiency. Without partition boards, a semi-analytical model combining a modified buoyancy ceiling jet theory and zone model was established to predict the key parameters at steady stage. The analytical predictions were compared with numerical results. 15 monitors were predesigned at an opening and the channels separated by the partition boards to collect the velocity and hydrogen concentration evolutions. The results show that the existence of the partition boards significantly promotes the ventilation efficiency by decreasing the hydrogen concentration in the confined space, constraining the flammable regime into a smaller volume, and increasing both the inflow and outflow velocities. Better ventilation efficiency is achieved by higher partition boards until a critical height after which no appreciable improvement can be gained. Applying the partition boards considerably shortens the developing stage of the dispersion process and intensifies the turbulence of outflow. Conclusions obtained in current work may benefit the natural ventilation system and building structure design for hydrogen safety in practical applications. (c) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.