Sensitivity of vegetation activity to water and temperature in eastern China was investigated using growing-season Normalized Difference Vegetation Index (NDVI) and climate factors (MAP, mean annual precipitation; RH, relative humidity; PDSI, Palmer Drought Severity Index; and MAT, mean annual temperature). At a regional level, the cut-off of mean NDVI value receiving a MAP interval of 543 ± 69 mm is identified, indicating the saturating effect of natural vegetation cover or greenness in the open-canopy summer-green deciduous forest of eastern China along the north–south rainfall gradient. The rainfall-use efficiency (RUE) of vegetation as well as correlation coefficients of NDVI against MAP, RH and PDSI decreases with increased precipitation in a consistent logarithmic pattern. In most cases, temperature does not have a significant effect on the vegetation activity. The results of this study highlight a clear pattern of water-dominated vegetation activity; however, a potential temperature-induced drought stress in temperate steppe and subtropical evergreen broadleaf forest of eastern China is also indicated.