<p>Sodium montmorillonite (Na-MMT) as a layered mineral renowned for its excellent ion exchange and adsorption properties plays a crucial role in various applications, including engineering slurries and catalysis adsorption. Therefore, a comprehensive study of its stability is essential for enhancing the overall stability of numerous composite materials. To investigate the enduring stability of this crystal from an atomic point of view, first principle density functional theory CASTEP software was used to calculate the Milliken population parameters, band structure, and density of states of Na-MMT crystals. The results demonstrate that the average bond populations of Si–O and Al–O bonds are 0.59 and 0.38, respectively, indicating strong covalent character and confirming their essential role in maintaining the structural stability of Na-MMT. Furthermore, the energy band diagram reveals a substantial forbidden bandwidth of approximately 4.49 eV, which signifies limited interatomic electron transfer, further fortifying the crystal's stability. Moreover, a pseudogap with the width of 6.82 eV is present in the total density of states diagram and corroborates the stability of the atomic bonding. The results above demonstrate the significant influence of molecular structure and electronic states on the macroscopic properties of Na-MMT crystals from a microscopic standpoint, which provides a solid theoretical foundation for the further application of this mineral’s stability in engineering slurry and other industrial fields.</p>