Rafting is a distinct characteristic of superalloys strengthened by L12-γ′ precipitates. Element migration during rafting of Co-10Al-7W (at.%) alloy is here investigated by phase-field simulation. The rafting direction is along the γ matrix channel with the higher Von Mises equivalent stress. In the γ channel, the compressive stress drives atoms of large size to migrate into a vertical channel with small elastic energy density under tensile strain, and the boundary dissolution of γ′ supplies solute atoms for the γ′ rafting connection in Co-Al-W-based superalloys. The junctions start at the corners of the γ′ precipitates where the larger stress is. Strain energy changes the compositions of γ and γ′ phases and results in an increase of lattice mismatch.