The ionization potential depression (IPD) is crucial for understanding the ionization processes of atoms and ions in plasmas. Many efforts have been devoted to exploring the temperature and the density dependence of IPD, leading to the development of models such as the Ecker-Kröll (EK) and Stewart-Pyatt (SP) models. However, these models fail to explain the plasma spectroscopy observed during laser nitriding process. To address the problem, the present study introduces a novel IPD model and the concept of mechanical-electric coupling (MEC) for the plasma. The MEC is important as it can influence a multitude of physical properties, including the diffusion of ionized electrons, Debye screening and the ionized electron pressure. The IPD model proposed herein is constructed based on spherical wave functions for the ionized electrons. It has been shown that this IPD model aligns well with both experimental spectroscopic data and the experimental IPD values for ions across various charge states. The integration of MEC with the IPD model may culminate in the formulation of an equation of state that is in concordance with experimental observations of the plasma behaviors. Overall, the MEC and IPD model proposed in this study could be instrumental for comprehending the ionization processes and the diverse properties of plasmas.