The Nanjing City Wall, a remarkable cultural heritage structure with over 600 years of history, faces challenges from environmental and climatic factors that contribute to its deterioration. A significant characteristic of the Nanjing City Wall is the abundant vegetation growing around the structure. While the aesthetic and ecological value of this vegetation is recognized, its role in the degradation or protection of the wall’s bricks remains poorly understood, creating a pressing need for scientific investigation. This study aims to address this knowledge gap by analyzing the impact of vegetation on the microclimate surrounding the wall and its effects on brick material deterioration. Using a combination of meteorological parameter monitoring and periodic weighing of detached material from the wall surface, we quantitatively compared the deterioration of wall bricks under two conditions: with and without vegetation shading. The results revealed the following: (1) Vegetation shading significantly stabilizes both heritage structure and its surrounding microclimate, effectively reducing wall surface temperature, fluctuations in thermal and humidity parameters, solar radiation, and precipitation. (2) The presence of vegetation does not consistently mitigate surface degradation, as deterioration rates varied between shaded and bare walls across different hygrothermal conditions. (3) Precipitation, humidity, and temperature emerged as key meteorological drivers of brick deterioration in spring. These findings highlight the need for careful assessment and management of nature-based solutions (NbS) in heritage environments.