This invention involves the new acetyl-CoA ligase gene (pclB) from Penicillium chrysogenum, its amino acid sequence and expression vector. It also demonstrated that the expression of pclB can be induced by the phenyl acetic acid. Then expression vector containing the pclB gene and the genetic engineering strain producing penicillin are constructed, the yield of penicillin of the transgenic strainis markedly improved. The invention is of great importance to the production of penicillin.