The evolution of the river systems in the Qilian Mountains is complex, shaped by a combination of factors, including tectonics, climate and lithology. While extensive research has been conducted on the regional tectonic evolution and surface processes, the evolution of internal drainage divides and trends in river system reorganization remain poorly understood. Under the influence of tectonic and climatic disturbances, drainage divides, as basin boundaries, continuously migrate, a process that can span tens of millions of years. Thus, the analysis of drainage divide stability provides new insights and constraints on understanding basin evolution mechanisms. This study evaluates the drainage divide stability of the Heihe River within the Qilian Mountains using the χ-plot and the Gilbert method. The results indicate that drainage divide stability varies across different parts of the basin, with a general pattern of synchronous expansion and contraction of the transverse and longitudinal rivers. The study reveals that the evolution of the Heihe River Basin is primarily controlled by regional tectonic evolution in the orogenic belt, with comparatively minor influences from climate, lithology and local fault activity. The evolutionary patterns observed in the Heihe River Basin offer valuable insights into the competitive dynamics between transverse and longitudinal rivers within orogenic belts and provide a new perspective on drainage reorganization in tectonically active regions.