The influence of pressure on the bubble size and average bed voidage has been investigated experimentally and computationally in a circular three-dimensional cold-flow model of pressurized jetting fluidized bed of 0.2 m i.d. and 0.6 m in height with a central jet and a conical distributor, which roughly stands for the ash-agglomerating fluidized bed coal gasifier. The pressurized average bed voidage and bubble size in the jetting fluidized bed were investigated by using electrical capacitance tomography (ECT) technique. The time-averaged cross-sectional solids concentration distribution in the fluidized bed was recorded. The influence of pressure on the size of bubble and the average bed voidage in a pressurized fluidized bed was studied. Both experimental and theoretical results clearly indicate that there is, at the lower pressure, a small initial increase in bubble size decided by voidage and then a decrease with a further increase in pressure, which proves the conclusion of Cai et.al. [P. Cai, M. Schiavetti, G. De Michele, G.C. Grazzini, M. Miccio, Quantitative estimation of bubble size in PFBC, Powder Technology 80 (1994) 99-109]. At higher pressure, bubbles become smaller and smaller because of splitting. The average bed voidage increases gradually with the pressure at the same gas velocity. However, there is a disagreement between the experimental results and simulation results in the average bed voidage at the higher gas velocity, especially at the higher pressure. It suggests that the increase in density of gas with pressure may result in the drag increase and the drag model needs to be improved and revised at higher pressure. (C) 2007 Elsevier B.V. All rights reserved.