Abstract: This study investigates a convective initiation event triggered by the intersection of convergence lines over the central Taihang Mountains of North China on July 31, 2019. Using high-resolution numerical simulation data, combined with diagnostic analyses based on the vertical motion equation and the buoyancy tendency equation, we explore the key dynamic processes governing the vertical acceleration that precedes convective initiation. Analysis of the vertical motion equation indicates that vertical acceleration is dominated primarily by the buoyancy term, with the perturbation pressure gradient force playing a modulating role. Backward trajectory analysis further reveals that the buoyancy term gradually weakens at low levels as horizontal convergence intensifies, but strengthens markedly after air parcels ascend to an altitude of 3.5 km. The buoyancy tendency equation shows that local buoyancy variations are regulated primarily by the stratification and three-dimensional divergence terms. The stratification term, arising from the decrease in ambient density with height, consistently inhibits the maintenance of positive buoyancy. In contrast, the three-dimensional divergence term exhibits a “convergence–divergence–convergence” vertical structure before convective initiation occurs. The vertical structure can be described as follows: three-dimensional convergence (dominated by horizontal convergence) below 2 km; three-dimensional divergence between 2 and 6 km (dominated by vertical divergence from 2 to 5 km and horizontal divergence from 5 to 6 km); three-dimensional convergence above 6 km. The low-level convergence and mid-level divergence configuration associated with this structure transports the mass converged at low levels upward via vertical motion and disperses it horizontally. Therefore, the mid-level atmosphere loses mass, and its density decreases. This process enhances positive buoyancy, thereby providing a sustained driving force for upward motion and favoring the development of vertical motion before convective initiation.