Abstract: Due to the fact that micropores prevent gas while pump liquid according to their capillary force characteristics, the tube with mesh construction inside is proposed to modulate flow patterns and enhance heat transfer. Based on Lockhart-Martinelli's separated flow model and Zuber-Findlay's drift model, one-dimensional mathematic model is built to describe the flow dynamic behaviors in vertical flow pattern modulated tube. The experimental conditions are solved by mathematic model and the relative errors between model predicted and experimental results are no more than 20%. It is noted that liquid velocity plays a more important role on flow phenomena than gas velocity while gas velocity influences the degree of penetration through the mesh. Based on qualitative analysis, cubic interpolation and least squares B-spline fitting are used to obtain the quantitative function relationship between flow phenomena and superficial velocity. It comes to the conclusion that when Re_l < 6937, there must be the first kind of condition, and when Re_l > 6937 with Re_g < 67, there can be the second kind of condition which is more likely to present at lower gas velocity. The mathematic model and quantitative function can contribute to the optimal design of flow pattern modulated tube.