Hydrodynamics of particle clusters suspended in viscous fluids is a subject of considerable theoretical and practical importance. Using finite volume method, drag forces of interacting coaxial sphere chain suspended in Herschel-Bulkley fluid flow are investigated numerically. The contribution of this paper is to determine the drag force of interacting spheres. The effects of yield stress and separation distance on drag forces are explored systematically. The present results suggest that the creeping flow assumption is still valid for finite Reynolds number Re while the yield stress is large enough (Od/Re > 10.0). For two spheres creeping flow, the interaction distance between each sphere is reduced with the increasing of the yield stress. For multi-spheres, the shielding and ending effects of the head and end spheres are significantly weakened due to the action of yield stress. (c) 2006 Elsevier B.V. All rights reserved.