To acquire the gas/particle flow characteristics of an in-assembly down-fired 600-MWe supercritical utility boiler, experiments were conducted by using particle dynamics anemometer (FDA) measurement within a two-phase small-scale model at various staged-air ratio settings (i.e., 0%, 6%, and 12%). The mean velocity, particle volume flux, and particle number concentration along several cross sections, were discussed well in the present work, in addition to the decay and trajectories of the downward gas/particle flow. For all three settings, asymmetric gas/particle flow characteristics appeared in the lower furnace, with the gas/particle flow in the front-half furnace penetrating greatly further and occupying much more furnace volume than that in the rear-half furnace. The longitudinal-velocity components are clearly higher near the front wall than near the rear wall. Decreasing the staged-air ratio can only weaken the gas/particle flow asymmetries to some extent. An estimation on the furnace performance, i.e., severe asymmetric combustion, low burnout, and high NOx emissions, is given out for the boiler's commercial operation in the near future. (C) 2012 Elsevier Ltd. All rights reserved.