Grazing has been shown to alter soil organic phosphorus (SOP) by affecting plants, microorganisms, and soil physicochemical properties. However, the mechanisms driving SOP responses and the interactive effects among these three ecosystem components remain largely unexplored. Here we investigated SOP response to long-term grazing, including control, light (LG) and heavy grazing (HG), in a desert grassland from Inner Mongolia. We separated SOP into labile (LOP), moderately labile (MLOP), and nonlabile organic P (NOP) fractions. Heavy grazing decreased MLOP by 25% (p<0.05) and marginally increased NOP by 15% (p = 0.055) without affecting LOP; LG and topography showed no notable impact on any fractions. We related the SOP results to plant (above-and below-ground biomass), key soil properties (nutrients, pH, moisture, and temperature), and phoD-harbouring bacterial communities (Shannon diversity and composition). Among the fractions, MLOP was the most responsive, significantly influenced by plant, soil properties, and phoD-harbouring bacteria, both individually and interactively. Soil LOP was solely influenced byphoD-harbouring bacteria, showing no notable associations with the other two variables, while NOP showed negligible changes. Specifically, MLOP was positively correlated with both above-and below-ground biomass, while negatively correlated with soil temperature. Soil LOP showed a significant positive correlation with the Shannon diversity of phoD-harbouring bacteria and soil available P. Overall, our findings highlight MLOP as the most environmentally responsive SOP fraction, and its interplay with LOP provides mechanistic insights into maintaining the stability of soil P supply in grazing semi-arid regions.