We discuss the evolution of single particle state (SPS) energies by the deformation within a deformed Woods–Saxon potential. Since the SPS energy (SPSE) is based on the concept of one-body potential, we decompose it into kinetic and potential energy, and consider the modification of total binding energy (TBE) beyond the one-body potential by the pairing correlations. Evolution of each energy is detailed numerically. The TBEs of nuclei in s–d shell are obtained in terms of the deformation by minimizing the TBE. Our results infer that a simple summation of the SPSE is not enough to explain experimental TBEs, so that we suggest how to properly obtain the TBE and the reasonable deformation beyond the deformed Woods–Saxon potential by including realistic pairing interactions by G-Matrix.