A series of new plasmids containing xylE gene was constructed based on the shuttle plasmid pTG 402 between E. coli and B. subtilis. The expressed xylE gene product catechol 2,3-dioxygenase (CatO2ase) was measured for its output and distribution, and analysed for its structural hydrophobicity and hydrophilicity. It was demonstrated that the output of CatO2ase was relative to plasmids, host cells, culture time and with or without induction. The enzyme didn't have features of excretional proteins and was mostly distributed inside the cells though a little could be detected in culture medium. It can be used as a selective marker, indicator and monitor in the study of genetic engineering. This research also provides a scientific basis for eliminating pollution of aromatic hydrocabonic compounds with genetic engineering bacteria.