In a 9.3 m high and 0.10 m i.d. gas-solids downflow fluidized bed (downer), the radial and axial distributions of the local solids holdups and particle velocities along the downer column were measured with the superficial gas velocity set to zero. A unique gas-solids flow structure was found in the downer system with zero gas velocity, which is completely different from that under conditions with higher gas velocities, in terms of its radial and axial flow structures as well as its micro flow structure. The gas-solids flow pattern under zero gas velocity conditions, together with that under low gas velocity conditions, can be considered as a special regime which differs from that under higher gas velocity conditions. According to the hydrodynamic properties of the two regimes, they can be named the "dense annulus" regime for the flow pattern under zero or low gas velocity conditions and the "dense core" regime for that under higher gas velocity conditions.