In a textile composite, a textile preform is used as the reinforcement phase instead of unidirectional or discontinuous fibers. Textile preforms can easily take the form of complex parts and the final part is a suitable alternative for conventional laminates, as the resultant part would be more efficient and reliable and sometimes the production cost is reduced. The arrival of textile composites in advanced industries such as aerospace, military, automobile, and sports, made a great evolution in them. Among the textile composites, braided composites are of great importance and they are used more extensively, as the braiding process can develop an integrated and firm structure. Braiding process can create complex preforms. In braiding process, two of the important factors in mechanical properties of final composite part is the braid angle and perpendicular spacing of yarns. In this research, first, the braiding process for round mandrels is modeled in finite element software, then the results are evaluated with experimental measurements. Next, the effect of mandrel dimensions on braid angles is studied using the models and experiments. In the next step, besides presenting new analytical relations for calculating braid angle of mandrels with flat faces, these mandrels are modeled and the braid angle and the perpendicular yarns spacing are measured for different mandrel aspect ratios. Also the effect of eccentricity of mandrel on braid angles of different faces is studied in the models and the eccentricity is controlled to reach the desired angles by optimization. Another approach is proposed for changing and controlling the braid angle which is changing the circular guide ring to an elliptic one. After modifying the analytical relations for elliptic guide ring, it is validated using modeling. In this step, a comprehensive code is generated to control the braid angles by changing the guide ring dimensions, the eccentricity, and the braid feed rate. The results are validated using experimental data and a solution is provided for keeping the mandrel in the correct place together with proper guide ring for experimental tests. With the help of preform properties such as braid angle and yarns spacing, and also micromechanical method, the mechanical properties of final composite is predicted. The results are compared with previous research to be validated. The results show that the analytical relations are fully correct and the effect of changing the dimension of mandrel on braid angle is negligible, while the effect of eccentricity of mandrel and the shape of guide ring is significant. The predicted braid angles by finite element analysis are in good consistence with experimental results and also the predicted mechanical behavior by Keywords: Composites made with tubular braiding, braid angle, Finite element modeling, Aspect ratio, Eccentricity, guide ring shape, Micromechanical analysis