The C-3 plant leaf wax delta C-13 (delta C-13(alk)) is commonly used to reconstruct past climates. However, our understanding of how precipitation and temperature influence terrestrial C-3 delta C-13(alk) is limited. To address this gap, we investigated the delta C-13 of n-C-29 alkane (delta C-13(29)) of C-3 terrestrial angiosperms in subtropical humid regions in China and compiled a global dataset. Results show a strong correlation between C-3 terrestrial angiosperms delta C-13(29) and mean annual temperature in both Chinese subtropical humid regions (r = -0.94, p < 0.001) and global humid zones (r = -0.78, p < 0.001). The linear fit lines of the regional and global datasets have similar slopes (-0.3129 vs -0.2896) and intercepts (-30.82 vs -31.41), indicating consistent responses to air temperature in global humid zones. When considering only sites with temperature data from meteorological stations, the correlation coefficient increases to -0.96 (p < 0.001) for the global dataset. In contrast to humid zones, mean annual precipitation significantly correlates with C-3 terrestrial angiosperms delta C-13(29) in arid zones (r = -0.75, p < 0.001), supporting the main controls of precipitation in these areas. These findings emphasize the impact of temperature on C-3 terrestrial delta C-13(alk), particularly in humid zones, and highlight caution when interpreting delta C-13(alk) in geological records under changing hydroclimate conditions or unstable settings.