The mechanisms of generation and transportation of a chemically active species in a tube generated by dielectric barrier discharge have been analyzed by experimental and computational methods to elucidate the sterilization mechanism. The obtained results are: i) Nitrogen oxide is an important sterilization factor. ii) Two‐dimensional profiles of emission intensities that expand between the wire and ground in a cross section of the tube were generated by streamer propagation and relaxation processes. iii) A twin vortex was induced in the cross section of the tube by the discharge. Chemically active species, probably transported from the discharge region to the upper region of the tube by the twin vortex, were concentrated by the circular flow.