Abstract: Transpiration cooling has been considered as a dissipation process of heat energy in trees for a long time. The direct result of transpiration cooling failure should be high leaf temperature. This paper aims to study the transpiration failure by monitoring the leaf temperature of sweetgum (Liquidambar styraciflua) with thermography. By measuring the water content, leaf imaging temperature, leaf stomata conductance and the RGB values in local area of same sweetgum leaves, transpiration failure was observed differentially after major veins severed. According to thermography analysis, significant high temperature area was early detected on the major veins severed sweetgum leaves. There was consistence among the lower water content, smaller leaf stomata conductance and reddened leaf lamina. This suggested that the persistent transpiration cooling failure induced the protective responses in the stressed area where is farthest to the water source and cause the red or purplish red area on severed leaves. By comparison, it significantly differs from characteristics which appeared on the similarly severed sasanqua camellia (Camellia sasanqua) leaves.