In this work, the 1-Li⁺, 1-Na⁺ and 1-K⁺ complexes formed by N-methylbenzoaza-18-crown-6-ether derivatives (1) with one alkali metal cation (Li⁺, Na⁺ and K⁺) were investigated. Significantly, the dipole moments of 1-Li⁺, 1-Na⁺ and 1-K⁺ enhance with increasing atomic number. However, their first hyperpolarizabilities (β₀) decrease with increasing the atomic number. Further results show that the interaction energies increase in the order of 1-Li⁺ > 1-Na⁺ > 1-K⁺. Moreover, the transition energies of 1-Li⁺, 1-Na⁺ and 1-K⁺ are inversely proportional to the β₀ values. Therefore, the interaction energy and transition energy are the major factors determining the β₀ values of 1-Li⁺, 1-Na⁺ and 1-K⁺. The combining of large variations of the dipole moment and the first hyperpolarizability can be used as a detection sensor for alkali metal cations. We hope that this work will provide valuable knowledge for designing alkali metal cation sensors by electro-optical properties.