This study developed the cyclone conveying system using roughage cutter for the round bale reported in the previous papers. Performance tests were conducted whether it can easily separate dust from roughage such as rice straws and it can transport roughages from cutter to TMR mixer. In addition, the airflow patterns in the cyclone conveying system were investigated using CFD code (FLUENT 6.2) for various velocities of dust collection fan. The cyclone conveying system was designed based on dried rice straws with a diameter of 1,340 mm, a cylinder length of 1,220 mm, a cone length of 850 mm and the current velocity of the dust collection fan was 15~20 m/s. It was found that transporting of roughage from cutter to TMR mixer and the separation of dust were satisfactory, and the dust removal rate of rice straws was around 31.9%. CFD analysis showed that, at the blowing fan velocity of 11.6 m/s, the airflow velocity inside the dust collector increased as velocity of the dust collection fan increased, but the airflow patterns inside the dust collector were all much the same.