This work systematically investigates the regulatory principles and underlying physical mechanisms of oxygen partial pressure (40%–100%) on the structure, defects, and electrical properties of Zn_0.6Mg_0.4O_(1-δ) ferroelectric films prepared by magnetron sputtering. The results indicate that the films deposited under oxygen partial pressures below 80% exhibit a columnar crystal structure with high crystallinity and a strong c-axis preferred orientation. Combined analysis of X-ray photoelectron spectroscopy (XPS) and photoluminescence spectroscopy (PL) reveals that oxygen partial pressure effectively modulates the types of intrinsic defects within the films, with high oxygen partial pressure significantly suppressing the formation of oxygen vacancies and metal interstitial defects. The reduction in the concentration of such defects leads to a lower leakage current of films and a marked improvement in its reliability. Ferroelectric characterization further indicates that, within the 60%-100% oxygen partial pressure range, the films exhibit excellent insulating properties and high breakdown field, enabling the observation of distinct switching current peaks in the transient current – electric field curves (I-E) curves, which confirms their ferroelectricity. The trend of decreasing remanent polarization with increasing oxygen partial pressure reveals that a highly consistent c-axis preferred orientation serves as the key structural foundation for achieving efficient polarization switching in wurtzite-structure ferroelectric films. Broadband dielectric spectroscopy effectively distinguishes the contributions of bulk polarization and surface polarization, confirming that the surface polarization contribution is enhanced under low oxygen partial pressure conditions. This work elucidates the synergistic mechanism through which oxygen partial pressure regulates the microstructure, defect types and concentrations, and macroscopic electrical properties of Zn_0.6Mg_0.4O_(1-δ) films, providing important guidance for their application in high-performance ferroelectric memory devices.