Abstract: Tree trunk whitewashing has long been practiced as a tree maintenance method in China's urban landscaping, yet the ecological rationality of its one-size-fits-all blanket implementation nationwide has long been highly controversial. Drawing on theories from plant physiology and soil ecology, and incorporating a case study of reform practices in Beijing, this paper systematically analyzes the comprehensive effects and applicable scope of trunk whitewashing. The results indicate that whitewashing provides only limited protective effects for newly planted saplings and vulnerable seedlings in cold regions of northern China. When applied in warm southern regions, or to mature large trees, and ancient and famous trees, it tends to cause tree damage, soil alkalization and microecological imbalance, with overall disadvantages outweighing advantages. Referring to the experience of Beijing, this paper proposes improvement countermeasures including classified management and control, ecological alternatives, and optimized assessment mechanisms, offering a reference for the scientific and cost-effective transformation of urban greening maintenance.