Abstract: Lattice Boltzmann simulations of flows past fixed monodisperse spheres are employed to obtain the drag force on spheres at low Reynolds numbers. The fixed spheres are comprised of center and surrounding parts. Spheres in the center part are distributed with structures, while those in the surrounding part are distributed in random homogeneous configurations. The results show that the solid volume fraction in the surrounding part (also referred to as “surrounding solid volume fraction”) has a significant impact on the drag force of the center particles. This drag variation due to the change of surrounding solid volume fraction becomes even larger as the solid volume fraction or the inhomogeneities of the central particles increase. A new drag model considering the surrounding influence is proposed and it is very promising in resolving the gas-solid interactions in flows with complex structures such as riser flows.