The microstructure of a [001] orientated single crystal Ni-based superalloy was observed during tensile creep. By the stress-strain finite element method (FEM) for calculating the von Mises stress distribution in the coherent interface of the cubic γ/γ′ phases, the influence of the applied stress on the regularity of γ′ phase directional coarsening was investigated. Results show that the distribution of the von Mises stress in the cubic γ/γ′ interfaces is changed by the applied tensile stress, which may bring the lattice contraction or expanding of the various crystal planes in the cubical γ′ phase. Thereinto, the lattice contraction strain on (001) plane may repel the Al and Ti atoms with bigger radius, while the lattice expanding strain on (100) and (010) planes may trap the Al and Ti atoms to promote the directional growth of γ′ phase into the mesh-like layer structure along the normal of the expanding lattice. This is thought to be the regularity of γ′ phase directional coarsening during creep of the alloy. Furthermore, the driving force of the elements diffusing and γ′ phase directional coarsening was proposed.