[en] Highlights: • The pentagonal CN₂ nanoribbon is stable both in kinetics and thermodynamics. • The CN₂ nanoribbon is a semiconductor with a direct band gap of 1.5 eV, and the energy band structure is spin splitting. • An applied external electric field can transform the pentagonal CN₂ nanoribbon from semiconductor to metal. Cutting two-dimensional (2D) CN₂ sheet along specific crystallographic orientations to construct CN₂ nanoribbon, its electronic structure is investigated systemically. We show by first-principles calculations that the electronic properties of CN₂ nanoribbon exhibit response to applied electric field and strain. The lowest conduction band and highest valence bands of the spin-up and spin-down states approach to the Fermi level respectively with increasing the strength of the electric field and tensile strain. More interestingly, an applied electric field can transform the nature of the CN₂ nanoribbon from semiconductor to metal. These results provides us an efficient way to design spintronic devices based on the CN₂ nanoribbons.