The influences of particle concentration and particle size distribution on particle behavior in hindered settling were investigated by a large-scale hybrid simulation involving a discrete element method for settling particles coupled with direct numerical simulation for fluid flow. The large-scale simulation is able to accept 100,000 particles with particle size distribution by using Earth Simulator. First, the simulation was carried out for the hindered settling of uniform size particles to confirm the reliability of proposed simulation method. The hindered settling velocity of particles decreased with increasing particle concentration, because of the increased drag force resulting from fluid flow induced by settling of particles. The relation between settling velocity of particles and particle concentration agreed with experimental observation. For hindered settling of particles with two different sizes, the influences of the volume fraction and size ratio of the larger to the smaller particles on settling velocity were investigated by the simulation. The settling velocity of particles of both sizes decreased as the volume fraction of larger particles and the particle size ratio increased, because of the increased fluid velocity caused by the settling of particles. In the laminar flow range, the influence of collision between settling particles was negligibly small, because the contact force between particles was extremely less than the drag force.