This invention involves the new encoding hydroxylase gene (pahB) from Penicillium chrysogenum, the gene encoding the peptide and containing the gene expression vector. It also demonstrated that the phenyl acetic acid can significantly induce the expression of pahB. The invention also provides a direction and target for increasing the production of penicillin from genitic modified Penicillium Chrysogenum, and is of great importance to the production of penicillin.