LaMnO3 has attracted significant attention as energy conversion and storage materials, and especially as a promising noble-metal-free oxide catalyst and a new kind of electrode material for supercapacitors. However, the poor electronic transport ability of LaMnO3 hinders its application. Thus, improvement of its electronic transport ability is essential to enhance the electron transfer from catalyst active sites to an electrode, which is effective to avoid ohmic potential drop and consequently energy loss. In this work, the high-quality epitaxial growth La-deficiency La0.9MnO3 films were obtained by a simple and low cost polymer assisted deposition method. It is found that the room-temperature conductivity (sigma) of doping La0.9MnO3 increases nearly ten times compared to that of the parent LaMnO3. The oxygen-content-driven enhancement of the conductivity is discussed for the oriented La0.9MnO3 film. It is suggested that the existence of the LaAlO3 substrate is beneficial to stabilize the La-deficiency La0.9MnO3 compound and A-site La-deficiency extends the range of oxygen content. Both strain (including epitaxial strain and doping induced chemical strain) and annealing temperature are cooperating on the oxygen content, resulting in the oxygen stoichiometry independence of ambient conditions and the high conductivity. Following this process, conductivity and electronic state of the perovskite-related material can be tuned for the practical application.