In this study, we chose Sr₂Co_xNb_2-xO_6-δ (SCN) as the electrode materials. Due to the similar radii size and small covalent difference between Co and Nb, cation disorder is intrinsic within this perovskite. A combination of first-principles and density-functional-theory (DFT) calculations was performed on both SCN and SCN with Co_Nb-Nb_Co antisite defects, focusing on the formation of bulk oxygen vacancies, which plays a pivotal role in oxygen ion diffusion process. It is found that the covalent states are +2, +3 and +4 for Co(most is +3, and the ratio of +4 is very small ) and +4 and +5 for Nb at their regular sites while in the antisite Co is +2 and Nb is +4. The oxygen vacancies formation energies follow the trend Co₃₊-O-Nb₅₊ >Co₂₊-O-Co₃₊ > Nb₄₊-O-Nb₅₊. The more electron delocalization between Co₂₊-O-Co₃₊ and Nb₄₊-O-Nb₅₊ is beneficial to weaken the electronic repulsion and stabilize vacancies. Therefore, we can see that higher degree of cation disorder can enhance oxygen ionic conductivity.