In the study, Cosmos sulphureus and Lantana camara was added into the field cultivating the vegetable Brassica chinensis L. (Crusiferea) in order to access the role of flower in attracttion and maintainance of natural enemies in the field. The experiments included four treatments: no adding flower (control), adding Cosmos sulphureus, adding Lantana camara, and the combination of both Cosmos sulphureus, Lantana camara. The result indicated that the densities of insect pest were significantly difference among the treatments in two different times of observation as P1=0,00 and P2 =0,00, respectively. Natural enemies have also significant difference among the treatments with P1=0,02 and P2=0.00, respectively. Some natural enemies such as Braconidae parasitoid, ladybug Harmonia axyridis, predatory mite, etc. were collected in the experiments. The roles of banker plant in maintain populations of natural enemies were discussed.