Over the last few years, the experimental and theoretical investigation regarding natural deep eutectic solvent (NADES) has gained more attention to unravel the behaviour behind the formation of eutectic solvent. The application domain of this solvent is also increased at the same pace, yet the mechanism of its formation is barely elucidated. The fundamental studies are limited to certain class of compounds which did not cover all the possible NADES species. This review aims to shed light on the formation mechanism of this novel solvent, which covers organic salt, organic acids, and alcohol-based NADES. The microstructure of NADES is found to form an extensive hydrogen bond network, considered one of the factors for this unique phenomenon. The hydrogen bonds are found to form at random hydrogen bond donor (HBD) and hydrogen bond acceptor (HBA) side, whereby the pattern is considerably similar for most classes of NADES. The molar ratio and species involved within the system also affect the resulting NADES, especially their physicochemical properties. This review provides insight into the binary and ternary system of NADES by highlighting the recent findings focusing on computational and theoretical work that utilise the quantum chemical and molecular dynamic approach.