Abstract: The equilibrium geometries and electronic structures of N₃^- and its ten isoelectronic systemshave been completely optimized and calculated by using ah toitio method. The relationship betWeen the electronic structure parameter and molecular stability was discussed in detail. It isfound that N₃^- have the following specialities in all isoelectronic system:the smallest orbital energy dchrence between HOMO and LUMO, the smallest N-N bond order and the sarial order of MO energy level. Thus, We came to the conclusion that N₃^- is very a non-stable system.