Under the more frequent and extreme global drought events, utilizing stable isotopes to quantify soil evaporation losses ( SEL) is of great significance for understanding the water supply capacity from soil to plants. From March 2017 to September 2019, we continuously monitored meteorological factors, soil temperature and humidity, and collected precipitation and soil water stable isotope data. Used the Craig-Gordon (C-G) model and the line-conditioned excess (lc-excess) couple with Rayleigh fractionation (RL) model to quantify SEL in subtropical secondary forests. The results showed: (1) The theoretical Evaporation Line (EL) slope correlated negatively with air temperature ( AT). Water source isotopic values were more positive in autumn and more negative in spring. The aridity index ( AI) and soil evaporation loss ratio ( f) from both models indicated drier conditions from March to September 2018 compared to 2017 and 2019; (2) Comparative analysis showed the C-G model agreed more closely with measured evapotranspiration ( ET₀) and water surface evaporation ( E) than the RL model, indicating its better suitability for the study region; (3) Because the “inverse temperature effect” of the precipitation isotopes, the linear fitting method was not suitable for determining the water source in spring, summer, autumn, and on the annual scale, while the EL slope obtained by the fitted slope was consistent with the basic principle of soil evaporation in winter. Thus, the theoretical method was more suitable for determining the EL slope in such regions; (4) because the different fundamentals, the C-G model was positively correlated with air temperature and negatively with relative humidity ( h), while the RL model showed the opposite, indicating different applicability. Meanwhile, SEL is influenced by soil thickness, atmospheric evaporation, and soil water supply capacities. These findings support using stable isotope techniques to quantify SEL and are important for analyzing soil water resources in subtropical secondary forests.