【Objective】The priming effect (PE) is a key process in regulating soil organic carbon dynamics, but its mechanism is complex and substrate dependent, which limits the accuracy of model predictions. Therefore, it is necessary to clarify its regulatory mechanism. 【Method】This study is based on 2 122 sets of global observational data, combined with meta-analysis, process-based model analysis, sensitivity testing, and random forest methods, to systematically analyze the mechanism, dynamic process, and main controlling factors of PE under different carbon substrate conditions. 【Result】The results show that: 1) Both simple and complex carbon inputs induce significant positive PE, but the intensity varies significantly among ecosystems, with farmland PE intensity (about 65%) significantly higher than forest ecosystems (about 33%). Multivariate analysis reveales that this difference is mainly due to the coupled variation of climate, soil physicochemical properties, and microbial community structure characteristics along environmental gradients. 2) The priming pathway exhibits significant substrate specificity. Simple carbon input mainly induces strong positive PE through microbial triggering effects, while complex carbon input mainly inhibits the decomposition of native soil organic matter and generates negative real PE through the substrate priority utilization mechanism. 3) The results based on the process model further indicate that the dynamic process of PE is controlled by substrate quality. Simple carbon inputs exhibit two patterns: “continuous positive” and “transient”, while complex carbon input is dominated by a “high apparent-negative real” pattern. Also, parameter sensitivity analysis shows that this model is mainly constrained by microbial maintenance metabolism, reflecting the differences in energy allocation strategies of microorganisms under different substrate conditions. 4) Besides, the main controlling factors of PE have hierarchical differentiation characteristics, and the apparent PE is mainly driven by microbial biomass carbon and soil carbon-to-nitrogen ratio. Moreover, the main controlling factors of real PE depend on substrate type. In simple carbon scenarios, soil organic carbon content and pH are dominant, while in complex carbon scenarios, the governing factors shift to soil carbon-to-nitrogen ratio and exogenous carbon addition. 【Conclusion】By elucidating the controlling mechanisms of PE under different carbon substrate input conditions, this study provides evidence for the accurate prediction of soil organic carbon and the assessment of soil carbon balance in the context of global climate change.