The experiment was designed based on consumption of carbon dioxide through the photosynthesis of Brassica oberacea var acephala leaf,and the photosynthesis of kale leaf under thallium stress was investigated by in situ attenuated total reflection FTIR (in situ ATR-FTIR).The ATR-FTIR showed that the absorption peaks of leaves had no obvious difference between plants growing in thallium stress soil and plants growing in non-thallium pollution soil,and the strong peaks at 3 380 cm^-1 could be assigned to the absorption of water,carbohydrate,protein or amide;the strong peaks at 2 916 and 2 850 cm^-1 assigned to the absorption of carbohydrate or aliphatic compound;the peaks at 1 640 cm^-1 assigned to the absorption of water.However,as detected by the in situ ATR-FTIR,the double peaks (negative peaks) at 2 360 and 2 340 cm^-1 that are assigned to the absorption of CO 2 appeared and became high gradually.It was showed that kale was carrying photosynthesis.At the same time,the carbon dioxide consumption speed of leaf under thallium stress was obviously larger than that of the blank.It was expressed that photosynthesis under thallium stress was stronger than the blank.All these represented that kale had certain tolerance to the heavy metal thallium.Meanwhile, the carbon dioxide consumption of grown-up leaf was more than that of young leaf whether or not under thallium stress.It was also indicated that the intensity of photosynthesis in grown-up leaf is higher than that in young leaf.