Based on annular transition threshold in Mandhane,through relating the selected threshold with the dimensionless criterion numbers by MATLAB software,a new dimensionless criterion formula of intermittentannular flow transition under oilgas lubrication condition.The rationality of this formula was tested by Fluent.A flow pattern transition map including stratifiedannular flow and intermittentannular transition was drawn by simulation.The research results show that the distribution discipline of oilgas phase in twophase flow simulated pattern is identical with the description of the pattern in the literature,the distribution discipline of pressure drop is agreed with previous conclusions.Because the diameter is smaller,the position of the transition curve about the new pattern map is lower than that in the Mandhane,but the trend of curve is basically the same as the Mandhand’s,so this pattern map provides the basis for studying pattern transition.