The electronic structure of ZnO and its native point defects has been calculated using full potential linear Muffin_tin orbital (FP_LMTO) method for the first time. The results show that Zn3d electrons play an important role in the bonding of ZnO. Vacant Zn (VZn) and interstitial O (Oi) produce the shallow acceptor levels at 0.3 eV and 0.4 eV above the top of the valence band (VB), while interstitial Zn (Zni) produces a shallow donor level at 0.5 eV bellow the bottom of the conduction band (CB). However, Vacant O (Vo) produces a deep donor level at 1.3 eV below the bottom of CB. On the basis of these results, we confirm that Zni is the main factor to induce the native n_type conductivity in ZnO.