The strain energy and strain element distribution of ZnSe/CdSe/ZnSe strained quantum well grown on vicinal GaAs(001) substrate are investigated by an atomic scale calculation based on valence-force field model. The strain distribution around the step edge is inhomogeneous, while that on the terrace is uniform and not different from just-oriented substrate. The largest strain energy is found at Cd atom at the step edge. The origin of the largest strain energy is shear deformation. The strain inhomogeneity extends for only 2 ML from the step edge in the vicinal direction. The lattice deformation extends to longer distance along the (111) direction than the (110) direction. Considerably large lattice-plane-tilting is caused by the shear strain in (110) plane. The tilt angle in CdSe lattice is more than 10 000 arcsec at the step edge, while that at terrace is less than 1000 arcsec. The lattice-plane-tilting also occurs on ZnSe layer top and below the step edge of CdSe, though the tilt angle is opposite to CdSe.