Li-O2 batteries with ultrahigh theoretical energy density have triggered worldwide research interests and hold the prospect for powering electric vehicles. However, the poor cycling stability and low energy efficiency of Li-O2 batteries still remain and hamper their practical application. Configuring desirable porous cathodes with uniformly dispersed and highly active catalysts is a noteworthy and feasible approach to overcoming these critical obstacles. Herein, we report on a novel strategy for the fabrication of Mn3O4 nanowires and carbon nanotubes composite film (Mn3O4/CNTs film) with ultrafine RuO2 nanoparticles (Mn3O4/CNTs-RuO2 film), in which the Mn3O4/CNTs film was employed as a conductive and porous matrix and extremely low amount of RuO2 (just 2.84wt%) are uniformly dispersed onto this matrix by using atomic layer deposition method, and reveal its electrochemical behaviors as a free-standing air electrode for Li-O2 batteries. The Mn3O4/CNTs-RuO2 film delivers a high specific capacity, improved round-trip energy efficiency and ultra-long cycle life (251 cycles). The superior electrochemical performance can be attributed to the enhanced catalytic activity of the grafted RuO2 with modulated electronic structure as the result of the interaction with substrate, which is evidenced by the corresponding X-ray absorption spectroscopy results and the unique nanosheet-shaped discharge product which can be smoothly decomposed.