The deformed potential structure of CdSe/ZnS core/shell quantum dots (QDs) was analyzed by calculating precise state energies and state functions. Exactly how an external electric field affects the photoluminescence was also studied. Additionally, the tilt potential structure induced by the external electric field, commonly referred to as the quantum-confined Stark effect, was calculated to account for the observed blue and red shifts. Experimental results indicated that the deformation also includes a bend, which is attributed to the shape of a QD. Calculations of the localization of electrons of the foregoing phenomena closely correspond to the experimental data.