Vacancy plays an important role in charge/discharge processes of solid-state lithium batteries because the vacancy-induced charge carrier trap and transportation channels effectively facilitate the diffusion of Li ion. Although lithium-rich layered oxide Li2TMO3 is a promising electrode material, it's vacancy mechanism remains unclear. In particular, the role of vacancy in the cycle life and electrochemical performance of Li2TMO3 is unknown. Here, we report on the volume variation (ΔV), average open circuit voltage (Voc) and electronic structure of Li2RuO3 layered oxide with various vacancies. Compared to Li-va vacancy, O-va (4.74 V) and Ru-va (4.60 V) vacancies enhance the Voc of Li2RuO3 (4.46 V) because O-va and Ru-va vacancies induced charge carrier traps improve the charge overlaps between the conduction band and valence band near the Fermi level. In particular, O-va vacancy is more thermodynamically stable than that of the other vacancies. Whether the perfect vacancy or vacancies after Li extraction, the calculated ΔV of O-va vacancy is smaller than that of the other vacancies. Therefore, we believe that O-va vacancy can improve the cycle life and electrochemical performance of Li2TMO3 layered oxides lithium batteries.