The near-field flow behavior of coaxial gas-liquid jets has a significant influence on the atomization performance and life cycle of atomizers, and the present study focused on this issue. The flow visualization technique was employed to examine liquid entrainment behavior near the nozzle. The thick central tube affected both gas and liquid flow fields. Liquid entrainment could be observed in the near-field with the increase in gas velocity, and a liquid "bulge" structure was induced on the surface of the near-field liquid jet for the first time. The formation mechanism and dynamic characteristics of the "bulge" were studied. Two critical situations in the liquid entrainment process to the surface of the central tube were identified as "initial entrainment" and "full entrainment". The two critical situations were studied in a convective gas-liquid layer in the recirculation region based on total pressure conservation theory. The theoretical models for the two situations were obtained, and these models agreed well with the experimental results. (C) 2013 Elsevier Ltd. All rights reserved