Abstract: 【Objective】The purpose of the study was to explore the effects of KOH modified tobacco stalk biochar on lead (Pb) and cadmium (Cd) absorption of flue-cured tobacco in Pb and Cd compsite polluted soil,in order to provide reference for using tobacco stalk biochar to improve soil polluted by heavy metals and reduce the risk of flue-cured tobacco heavy metal pollution.【Method】The experiment was conducted in pots to simulate the compsite pollution of Pb and Cd in tobacco-planting soil environment.Two factors,the compsite pollution concentration of Pb and Cd (PC) and the amount of biochar (T),were set.The concentrations of Pb and Cd were 0 and 0 mg/kg (PC0),30 and 500 mg/kg(PC1),and 60 and 1000 mg/kg (PC2),respectively.The amount of modified tobacco stalk biochar (carbon/soil mass ra-tio) was 0 (T0),2%(T1) and 4%(T2).There were nine treatments.Samples were taken 60 d after transplanting,and the dry matter accumulation,Pb and Cd contents and accumulative amounts of tobacco plants under different treatments were measured,and the enrichment coefficient and transport coefficient of Pb and Cd were calculated.【Result】Under the compsite pollution level (PC1 and PC2),the application of modified tobacco stalk biochar could reduce the dry matter accumulation of tobacco plants,and the reduction amplitude increased with the increase of the application amount of modified biochar.Under the same pollution level,Pb and Cd contents in all organs of tobacco plants were significantly decreased with the increase of application amount of modified tobacco stalk biochar (P<0.05,the same below).Among them,Pb contents in roots,stems and leaves of tobacco plants treated with PC1T2 were decreased by 75.60%,46.17%and 66.63%respectively compared with PC1T0 treatment.Cd contents decreased by 82.29%,74.97%and 77.67%respectively.Compared with PC2T0 treatment,Pb contents in roots,stems andleaves of tobacco plants treated with PC2T2 were decreased by 56.96%,62.90%and 69.83%respectively,and Cd contents were decreased by 76.80%,70.84%and59.13%,respectively.After the application of modified tobacco stalk biochar,Pb and Cd accumulation and enrichment coefficient in tobacco plants also showed a decreasing trend.Compared with PC1T0 treatment,the total Pb and Cd accumulation of tobacco plants in PC1T2 treatment was significantly reduced by 71.54%and 83.90%,and the enrichment coefficient was significantly reduced by 64.35%and 72.32%respectively.Compared with PC2T0 treatment,the total accumulation of Pb and Cd of tobacco plants were significantly decreased by 68.13%and 77.49%respectively,and the enrichment coefficients were decreased by 41.23%and 25.71%respectively.At a certain pollution level,the application of modified tobacco stalk biochar could inhibit the transfer ability of Pb and Cd from soil to the root system of tobacco plants.Among them,the TF_soil-root of Pb and Cd under PC1T2 treatment were significantly reduced by 68.00%and 76.44%compared with PC1T0 treatment respectively.The TF_soil-root of Pb and Cd in PC2T2 treatment were significantly reduced by37.93%and 45.55%compared with PC2T0 treatment respectively.【Conclusion】Application of KOH modified tobacco stalk biochar in Pb and Cd composite polluted tobacco-planting soil can inhibit the absorption of Pb and Cd by tobacco plants,effectively reduce the content and accumulation of Pb and Cd in tobacco plants,and alleviate the toxic effect of Pb and Cd compsite pollution on tobacco plants.