Abstract: 【Objective】To analyze the drought tolerance function of faba bean S-adenosylmethionine synthetase（SAMS） gene（VfSAMS2），which could provide reference for the selection and breeding of drought-tolerant varieties of faba bean and the analysis of the molecular mechanism of drought tolerance in plants.【Method】Based on the transcriptome information of faba bean drought stress，the VfSAMS2 gene was screened out from it in response to drought stress，the VfSMAS2 gene was overexpressed in tobacco using viral expression vectors，and natural drought stress was simulated through pot experiments. The drought tolerance phenotype of VfSAMS2 overexpressing tobacco lines was observed，and the water loss rate，proline（PRO）and malondialdehyde（MDA）contents，superoxide dismutase（SOD）and peroxidase（POD）activities，ethylene synthesis precursor l-aminocyclopropane-l-carboxylic acid（ACC），putrescine（Put），spermidine（Spd） and spermine（Spm）contents were measured in leaves before and after drought stress treatments，as well as the expression of genes related to the ethylene and polyamine pathways，such as 1-aminocyclopropane-1-carboxylic acid oxidase （ACO），S-adenosylmethionine decarboxylase（SAMDC），spermidine synthase（SPDS），spermine synthase（SPMS） and polyamine oxidase（PAO），which were involved in the regulation by SAMS.【Result】The coding region（CDS）of VfSAMS2 gene with a length of 1173 bp was amplified by PCR using faba bean seed cDNA as template，and was ligated into the viral expression vector PVX-LIC and then transformed into Agrobacterium rhizogenes GV3101. Agrobacterium rhizogenes GV3101 solution containing PVX-LIC-VfSAMS2 plasmid was injected into the abaxial surface of tobacco leaves with a syringe，while the injected leaves with Agrobacterium rhizo genes GV3101 solution the transformed the empty vector（PVX-LIC）were used as a control，and drought treatment was simulated by the complete water loss method. At 10 d of drought stress，the transformed empty vector tobacco leaves were found to be yellow and severely wilted；while the VfSAMS2 overexpressing tobacco leaves were only mildly wilted on the bottom leaves. Under drought stress，the water loss rate of in vitro VfSAMS2 overexpressing tobacco leaves was extremely significantly lower than that of transformed empty vector tobacco leaves after 1.0 h at room temperature. The MDA content of VfSAMS2 overexpressing tobacco leaves was not significantly different from that of transformed empty vector tobacco at 10 d of drought stress，the PRO content of VfSAMS2 overexpressing tobacco leaves was significantly reduced by 56.7%（P<0.05，the same below）and the POD activity was significantly increased by 154.2% compared with that of transformed empty vector tobacco. At 10 d of drought stress treatment，the ACC content of VfSAMS2 overexpressng tobacco was significantly reduced by 66.69% compared with that of transformed empty vector tobacco，and Put and Spm contents were significantly increased by 71.51% and 32.53% respectively compared with that of empty vector tobacco. The relative expression of the ACO gene in VfSAMS2 overexpressng tobacco was significantly reduced by 64.7% compared with that of transformed empty vector tobacco，and the relative expression of SAMDC，SPMS and PAO genes was significantly up-regulated by 24.3%，133.5% and 43.3% respectively compared to empty vector tobacco.【Conclusion】VfSAMS2 overexpression in tobacco improves drought tolerance by reducing ethylene synthesis，increasing the accumulation and oxidative decomposition of Spm，and enhancing POD activity.