In order to obtain a more precise gas-liquid two-phase flow pattern transition bounds within the slanted pipe, gas-liquid two-phase stream tests were carried out in a natural organic tube at the angles of 30°, 45°, 70° and 90° respectively. Besides, the organic tube is 40 mm in inner diameter and 8 m in length. The flow pattern under different working conditions are recorded, and the results of the test were compared with the flow pattern transition bounds of the Barnea. The research findings show that the bubble flow and slug flow areas in Barnea’s flow pattern map were not in line with the test results. In view of the above problems, this paper corrects the above flow pattern transition criterion, determines the more precisely bubble, churn and slug boundaries, and plots the redressed flow pattern chart, thus providing a more precise judgment criterion for the gas-liquid two-phase flow pattern at diverse slant points.