Atomic geometry, electronic structure and formation energy of native defects in Zn 3 N 2 films have been studied by means of density functional theory to interpret the different behaviors of defective Zn 3 N 2 . The effects of the vacancy and self-interstitial N on electronic and optical properties of zinc nitride were investigated, from which we conclude that N vacancy is responsible for n-type conduction character. Various defects may cause energy shift or gap change, which explains different optical band gap detected in Zn 3 N 2 samples.