This study examines the herbaceous plant community along the Jiulongtan section of the Yangtze River in the urban area of Chongqing, located at the core of the Three Gorges Reservoir area. It investigates the response mechanisms of herbaceous plant functional traits to complex water level fluctuations within the reservoir and analyzes competitor, stress-tolerator and ruderal (CSR) strategies and community construction mechanisms under environmental stress conditions. Differences in inundation time and intensity due to water level changes had significant effects on dominant species, species composition, life type, and diversity indices at all elevations. Understanding these changes is crucial for managing plant communities in fluctuating environments. This highlights the importance of understanding the complex relationship between environmental factors and plant adaptation. The results reveal that within the urban riparian zone of the Three Gorges Reservoir area, the Shannon-Wiener diversity index, Simpson’s dominance index, and Gleason’s species richness index tend to increase with altitude, while the Pielou’s evenness index shows a trend of initially decreasing followed by increasing. There are significant positive correlations between specific leaf area (SLA) and specific root length (SRL) with altitude, indicating that herbaceous plants increase leaf area and root length as altitude rises to enhance resource acquisition efficiency. Leaf dry matter content (LDMC) is significantly negatively correlated with altitude, indicating that herbaceous plants in lower-altitude inundation zones develop thicker leaves to cope with flooding stress. These functional traits proved to be the most sensitive to dynamic water level changes and are crucial for screening plants adapted to urban riparian zone conditions. The plant community mainly exhibits a stress-tolerant (S) strategy, with a notable presence of stress-tolerant-ruderal (S/SR) mixed strategy. Plants exhibited diverse CSR strategies at different elevation transects. The proportion of S-strategy plants initially decreases and then increases with altitude, while the proportion of ruderal (R) strategy plants firstly increases and then decreases; competitive (C) strategy plants maintain the lowest proportion. These results indicate that plants adjust SLA, SRL, and LDMC, along with the combination of these traits across different altitudinal gradients. This adaptation reveals how plants resist the physical disturbances induced by water level changes to optimize their adaptability and accordingly adjust their CSR strategy. The study preliminarily establishes a response mechanism for herbaceous plants in the urban riparian zone of the Three Gorges Reservoir Area to water level fluctuations. These findings provide an important theoretical and practical basis for developing stable herbaceous plant communities and sustainable management strategies for the urban river landscapes of the Three Gorges Reservoir area.