Three-dimensional(3-D) braiding technology using high-performance fibers for advanced composite structures is receiving great attention as a result of the outstanding mechanical and thermoelastic properties of the materials produced. A continuous and automatic 3-D circular braiding machinery system has been established at North Carolina State University. Structural geometries of the preforms such as the orientation angle, preform thickness, and yarn volume fraction are analyzed and discussed in accordance with the processing parameters of the machine. The convergent line of the 3-D braided preform on the mandrel is derived with mandrel diameter, traverse velocity, carrier angular velocity, and preform contour thickness. Mathematical relations between the structural parameters and machine-operating conditions are derived. The food agreement between the experimental observations and the theoretical predictions confirms the validity of the processing model developed.