In order to understand the mechanism of the effect of Cd pollution on photosynthesis,quality and yield of tobacco leaves,pot experiments were carried out at the Research Station of Henan Agricultural University during 2002～2004.Soil having a pH value of 7.5 and containing 8.53 g•kg^－1 organic matter,0.89 g•kg^－1 total N,20.42 mg•kg^－1 olsen-P,238 mg•kg^－1 NH4OAc-K,and 0.11 mg•kg^－1 Cd was used in the experiments.15 kg of sieved soil was placed in each 36 cm×42 cm pot.Fertilizers used were (NH₄)₂SO₄、KNO₃ and KH₂PO₄.Prior to sowing 3 g of N,4.5 g of P₂O₅ and 9 g of K₂O were applied to each pot.The cultivar used in the experiments was Yunyan 85,with 20 leaves left after topping.The liquid Cd(Ac)2 was applied to each pot as sewage with concentrations of 3,6,10,30,60 and 100 mg•kg^－1 after transplanting. Clean water was used as comparison.The experiment was arranged in a completely randomized design with three replications.The net photosynthetic rate (Pn),intercellular CO2 concentration (Ci) and stomatal conductance (Gs) of three identical functional leaves from the same position were determined during rosette,budding and harvest stages using a portable photosynthetic system (Li-6400). Maximal fluorescence (Fm)，fixed fluorescence (Fo)and steady fluorescence (Fs) were determined after 30-minute dark adaptation while maximal fluorescence in the light (Fm′) was measured after a certain length of light period (Hansatech FMS2 fluorometer).The same portion of each leaf was used for both kinds of measurements．PS Ⅱ activity(Fv／Fo)，PSⅡ maximum light energy transformation (Fv／Fm)，chemical quenching coefficient(qP), non-photochemical quenching coefficient (NPQ),the apparent photosynthetic electron transport rate (ETR) and the ratio of photochemical quantum yield of PSⅡ （Ф_PSⅡ） were calculated according to the following formulas：Fv／Fo=(Fm-Fo)／Fo，Fv／Fm=(Fm-Fo)／Fm，qP=(Fm′-Fs)／(Fm′-Fo)，NPQ=(Fm-Fm′)/ Fm′， Ф_PSⅡ=(Fm′-Fs)/Fm′，ETR=（Fm′-Fs）/Fm′×PAR×0.5×0.84．The contents of reductive sugar,total N,nicotine and Kalium in tobacco leaves and yield per plant were determined according to standard methods in the literature．The results showed that the net photosynthetic rate (Pn),stomatal conductance (Gs), PS Ⅱ activity(Fv／Fo)，PSⅡ maximum light energy transformation (Fv／Fm)，chemical quenching coefficient (qP),non-photochemical quenching coefficient (NPQ),the apparent photosynthetic electron transport rate (ETR) and the ratio of photochemical quantum yield of PSⅡ （Ф_PSⅡ）decreased with the increase in Cd concentration,while intercellular CO2 concentration Ci) behaved oppositely.The fact that the reductive Sugar/Nicotine ratio and Total-N/Nicotine ratio increased as the result of enhanced Cd pollution, has led to inharmonious chemical constituents in tobacco leaves and unpleasant aroma from them.