Density functional theory within the local density approximation is used to investigate the effect of the oxygen vacancy on the LaGaO3/SrTiO3 (001) heterojunction.It is found that the energy favorable configuration is the oxygen vacancy located at the 3rd layer of the STO substrate,and the antiferrodistortive distortion is induced by the oxygen vacancy introduced on the SrTiO3 side.Compared with the heterojunction without introducing oxygen vacancy,the heterojunction with introducing the oxygen vacancy does not change the origin of the two-dimensional electron gas (2DEG),that is,the 2DEG still originates from the dxy electrons,which are split from the t2g states of Ti atom at interface;however the oxygen vacancy is not beneficial to the confinement of the 2DEG.The extra electrons caused by the oxygen vacancy dominantly occupy the 3dx2-y2 orbitals of the Ti atom nearest to the oxygen vacancy,thus the density of carrier is enhanced by one order of magnitude due to the introduction of oxygen vacancy compared with the density of the ideal structure heterojunction.