Theoretical study of the electronic structure, nonlinear optical properties (NLO), and natural bonding orbital (NBO) analysis of 18-crown-6 were investigated using Density Functional Theory (DFT) calculations at the B3LYP/6-311G (d,p) level of theory. The optimized structure is nonlinear compound as indicated from the dihedral angles. Natural bonding orbital analysis have been analyzed in terms of the hybridization of each atom, natural charges (Core, Valence and Rydberg), bonding and antibonding orbital's second order perturbation energy (E(2)). The calculated EHOMO and ELUMO energies of the title molecule can be used to explain the charge transfer in the molecule and to calculate the global properties; the chemical hardness (η), softness (S), global electrophilicity index () and electronegativity (χ). The NLO parameters: static dipole moment (µ), polarizability (α), anisotropy polarizability (Δα), first order hyperpolarizability (βtot) and third-order hyperpolarizability ⟨γ⟩, of the studied molecule have been calculated at the same level of theory. The molecular electrostatic potential (MEP) and electrostatic potential (ESP) for the title molecule were investigated and analyzed. Also the electronic absorption spectra were discussed by time-dependent density functional theory (TD-DFT) calculations in ethanol and water solvents. From the experimental conductance measurements, the association thermodynamic parameters (KA, ∆GA, ∆HA and ∆SA) and complex formation thermodynamic parameters (Kf, ∆Gf, ∆Hf and ∆Sf) of nano-CuSO4 in presence of 18-crown-6 as a ligand in 10% ethanol – water solvents at different temperatures (298.15, 303.15, 308.15 and 313.15K) were applied and calculated.