In order to enhance the understanding of the spatiotemporal evolution of soil moisture in the subtropical monsoon climate region, the study focuses on Yunnan and its surrounding areas (90°-107°E, 15°-30°N). Utilising ERA5-Land reanalysis soil moisture data and employing various statistical methods such as Theil-Sen Median trend analysis and Mann-Kendall (M-K) non-parametric test, this research analyses the spatiotemporal variations of soil moisture in the Indochina Peninsula and its response to hydrothermal changes, exploring the responses of different soil moisture levels to climate change. The results indicate: (1) During the study period (1950-2020), the study area experiences alternating dry and wet soil moisture conditions, with drier years concentrated in 1955-1961 and 2001-2020, and wetter years mainly distributed in 1951-1954, 1961-1968, and 1971-1978. After entering the 21st century, soil drying becomes more pronounced, with positive anomalies in soil moisture at different depths from January to December, and a stronger drying trend during the dry season for SM1 to SM3. (2) Between 1950 and 2020, there is a clear dry-wet axis in the study area’s soil moisture, with the difference between the dry and wet axes decreasing with depth, and a trend of narrowing dry axis bands and expanding wet axis bands. (3) In the first and last years of the study period, soil moisture remains stable in most regions of the study area, with only 21.4% to 26.2% of the area experiencing drying, primarily transitioning from the (0.4, 0.45］ interval to the (0.35, 0.4］ interval. (4) There is significant spatial heterogeneity in soil moisture changes at different levels, with an overall weak drying trend. Of the area, 37.7% to 61.5% experiences soil moisture changes ranging from -0.001 to 0 m³·m^-3·10a^-1, and areas with increasing soil moisture are less than 20%. (5) After entering the 21st century, soil moisture in most months of the dry season becomes drier compared to earlier periods, with abrupt changes occurring in 2003 and 2008. (6) The temporal-latitudinal mean high-value centre of soil moisture extends with the increase in soil depth, and the high-value centre of soil moisture expands northward (eastward); the overall variation in soil moisture increases with latitude (longitude), and the seasonal differences in soil moisture decrease with depth and latitude (longitude). (7) The impact of evapotranspiration, precipitation, soil temperature, and Normalised Vegetation Index (NDVI) on soil moisture has a lag of 1 to 5 months. Apart from the negative correlation with NDVI, soil moisture is significantly positively correlated with the other three climate factors. Soil moisture is synergistically influenced by environmental factors, among which precipitation has the strongest impact on soil moisture.