Hydrodynamic interactions between particle pairs are studied following sedimentation theory. For two spheres, interactions are directly obtained through the resistance matrix which links interaction forces to particle relative velocities. For more than two spheres, the mobility matrix is estimated with a four order approximation on the particle distance, and then it is inversed to get the resistance matrix. A set of motion equations (coupled by the resistance matrix) is then solved to describe the particle behaviours. Results for sedimenting particles and collisions in low turbulence field are presented.