Abstract: In order to learn more about the connections between the expression levels and the yield of the key enzymes in 2,3-BD synthesis route. In this study the Acetolactate Synthase gene (budB) from Klebisella oxytoca HD79 was amplified by PCR with primers designed according to the sequence of budB in Gene Bank, which is 1680bp. The multicopying integrated expression vector pR1SW-budB was constructed using expression vector pRSFDuet-1 as a framework by meas of genetic engineering. The plasmid pR1SW-budB was transformed into Klebisella oxytoca HD79 by electric conversion, then screened through high concentration Kan and PCR for double characterization and transformants were carried out on the determination of enzyme activity. The result demonstrated that integration of expression vector of acetolactate synthase gene was constructed successful. ALS was mostly expressed with the activity of 1.0627 U/mg, which was improved for 4.35 times. That the yield of 2,3-BD as well as lay the foundation of the industrialization of 2,3-BD production in some degree.