Structure of staple yarns is an important factor that decides the physical and mechanical properties, which is dependent on the yarn formation mechanism. To improve the mechanical performance of the friction spun yarn and the manufacturing efficiency, this study dealt with structural characteristics of the O.E. friction spun yarn on the basis of the fiber trajectories, packing density, and orientation angle distribution. The influence of the twist on the yarn structure and yarn surface hairs also was investigated by applying the trace fiber method. Results show that the constituent fibers lie inside the yarn with uniform changes of the radial position along the yarn axis. The packing density shows the lowest value at the yarn center, while the density reaches the highest value at about between 2/3 and 4/5 of the yarn radius. Twist increase leads to the migration increase, which reduces the hairiness of the friction spun yarn.