A thorough understanding of the collision motions and involved hydrodynamic behaviors of double emulsion droplets under the influence of an external flow is important for the design and fabrication of a core-shell structured chemical product via droplet-based fluidic processing. In this study, experimental observations are combined with numerical simulation to analyze the hydrodynamic binary collision between double emulsion droplets under shear. The passing-over motion of the colliding droplets is observed and quantitatively characterized by providing the motion trajectories and temporal droplet deformation. In particular, because of an additional interaction induced by the inner droplet, we demonstrate that the double emulsion droplets exhibit similar motion trajectories but different deformation development versus ordinary single-phase ones throughout the collision process. Additionally, the increase in confinement (i.e. the decrease in spacing gap between two parallel moving walls in the typical Couette shear geometry) is found to induce a higher shear rate and larger elongational components at the tips of the deformed double emulsion droplets, which produce further stretched colliding droplets. (C) 2018 Elsevier Ltd. All rights reserved.