Abstract: In the 3-D braiding procedure, the braiding yarn is tended to move along the direction of its carrier movement. Based on the movement of carriers, this paper presents a control region method to analyze the yarn traces systematically in 4-step 3-d tubular braided preforms. Then, four interior cells and two surface cells are established. For the whole structure of the preform, it can be assembled by these unit cells. The geometry of each cell is deeply dependent on its position in the cross-section of the preform. All cells are oriented in the same reference frame as the preform, which is quite suitable for the analysis of the mechanical properties.