Oxygen incorporation is a widely used method for depositing high-quality CVD diamond films at low temperatures. However, this process inevitably introduces oxygen-terminated surfaces during diamond growth. Although the electronic properties and applications of oxygen-terminated surfaces have been extensively studied, their influence on the diamond growth process remains underexplored. Current research attributes the promotion of diamond growth by the oxygen‑incorporation process to the effect of oxygen in the gas phase on growth reactions. These theoretical models still assume the hydrogen‑terminated diamond surface as the basic environment for growth reactions, neglecting changes in the surface termination configuration of diamond. Therefore, investigating the effect of hydrogen-oxygen co-terminated diamond surfaces on diamond growth can complement existing theories and provide critical guidance for optimizing the oxygen-incorporation process in CVD diamond fabrication. In this study, first‑principles calculations were employed to investigate how hydrogen‑oxygen co‑terminated surfaces with varying oxygen coverage influence diamond growth. Using Materials Studio software, (100)‑2×1 diamond surfaces with oxygen coverage levels of 0%, 12.5%, 25% and 37.5% (denoted as dia0, dia1, dia2, and dia3, respectively) were constructed. On these four co‑terminated surfaces, two types of hydrogen‑abstraction reactions—one mediated by hydrogen atom and the other by hydroxyl group—as well as the adsorption of active methyl group (CH₃) were simulated. The results reveal that the presence of terminating oxygen modifies the electronic structure and dipole moment of the diamond surface, thereby affecting the generation of active sites and subsequent diamond growth. While the adsorption energy of hydrogen atom is only slightly influenced by terminating oxygen, the adsorption energy of hydroxyl group decreases significantly as surface oxygen coverage increases. Furthermore, the energy barriers for both abstraction reactions rise continuously with increasing oxygen coverage on hydrogen‑oxygen co‑terminated surfaces, indicating that the generation of active sites—whether initiated by hydrogen atom or hydroxyl group—is suppressed. In contrast, the adsorption of CH₃ is less affected by variations in oxygen coverage: although the adsorption energy of CH₃ increases slightly with higher oxygen coverage, this weak promotional effect is insufficient to offset the impediment to active‑site formation. In summary, the presence of terminating oxygen on diamond surfaces hinders the occurrence of abstraction reactions and the generation of active sites, thereby inhibiting the diamond growth process. Moreover, the degree of inhibition increases with increasing oxygen coverage. Therefore, precise control of surface oxygen coverage is essential for optimizing the oxygen‑incorporation process in CVD diamond fabrication.