The domain wall structure of ferroelectric/ paraelectric superlattices can be much more complex due to the influence of the superlattice stacking structure, the in-plane strain induced by the substrate and environmental temperature. In this study, we employed a phase field model to investigate the domain wall state of the SrTi${\mathrm{\text{O}}}_3$/BaTi${\mathrm{\text{O}}}_3$ superlattice structure. The domain wall thickness for the SrTi${\mathrm{\text{O}}}_3$/BaTi${\mathrm{\text{O}}}_3$ layer was measured using a hyperbolic function. Based on the simulation results, here, we show a domain wall state diagram to distinguish the hard and soft domain states. The polarization profiles across hard/ soft domain walls were illustrated and analyzed. Our simulation results offer a useful concept for the control of the domain wall state in the ferroelectric superlattice.