Abstract: Experiments were carried out to measure the wall shear stress(WSS) of air-water bubbly flow in the entrance region in a horizontal tube I.D.35 mm with TSI-1268W hot-film probes, and the wall shear stress data at different points in different sections were obtained and used to determine the development length.It was found that the discrete degree of WSS data increased due to introducing bubbles into the liquid.The development length was 52D—65D and increased with increasing liquid Reynolds number and void fraction.Due to the asymmetric distribution of bubbles in the horizontal tube, introducing bubbles made the wall shear stress change differently at different measuring points.