Understanding soil moisture dynamics is essential for predicting hydrological responses to climate extremes. Yet, the mechanisms regulating soil water infiltration and retention across diverse vegetation types in subtropical regions remain poorly understood. This study investigated soil moisture dynamics and rainfall infiltration across four predominant vegetation types in subtropical Southwest China: primary evergreen broadleaf forest, secondary Populus forest, managed tea plantation, and natural grassland. Volumetric soil moisture content was measured at five depths (10 cm to 100 cm) at 30-minute intervals from 2019 to 2022. The results revealed distinct soil moisture dynamics among vegetation types. During the rainy season, the tea plantation exhibited the highest soil moisture content, whereas the evergreen broadleaf forest maintained the highest moisture levels during the dry season. In contrast, the grassland consistently displayed the lowest soil moisture throughout the year. Temporal variability in soil moisture was more pronounced in the grassland and tea plantation compared to the Populus and evergreen forests. The vertical distribution of soil moisture varied significantly among vegetation types. Furthermore, cumulative infiltration was lower in the evergreen and Populus forests than in the grassland and tea plantations, underscoring the strong influence of vegetation type on infiltration and soil moisture retention. Crucially, the evergreen broadleaf forest maintained higher soil moisture levels and slower infiltration rates, highlighting the critical role of primary forests in sustaining soil moisture and enhancing regional drought resistance. The study provides valuable insights into the hydrological functions of different vegetation types in subtropical ecosystems and emphasizes the urgent need for enhanced conservation efforts to protect primary forests, especially given escalating climate change and drought risks.