LaMnO3 (LMO) films are deposited on SrTiO3:Nb (0.8 wt%) substrates under various oxygen pressures to obtain different concentrations of oxygen vacancies in the films. The results of X-ray diffraction verify that with a decrease of the oxygen pressure, the c-axis lattice constant of the LMO films becomes larger, owing to an increase of the oxygen vacancies. Aberration-corrected annular-bright-field scanning transmission electron microscopy with atomic resolution and sensitivity for light elements is used, which clearly shows that the number of oxygen vacancies increases with the decrease of oxygen pressure during fabrication. Correspondingly, the resistive switching property becomes more pronounced with more oxygen vacancies in the LMO films. Furthermore, a numerical model based on the modification of the interface property induced by the migration of oxygen vacancies in these structures is proposed to elucidate the underlying physical origins. The calculated results are in good agreement with the experimental data, which reveal from a theoretical point of view that the migration of oxygen vacancies and the variation of the Schottky barrier at the interface with applied bias dominate the resistive switching characteristic. It is promising that the resistive switching property in perovskite oxides can be manipulated by controlling the oxygen vacancies during fabrication or later annealing in an oxygen atmosphere.