Abstract: In order to decrease power consume of fan in 4ZTL-1800 combine harvester threshing prior to cutting with air suction, traces of chaffies and short straws moving in the fan were tracked by discrete phase model of Lagrange in numerical simulation. Their moving laws were as follows. Chaffies and straws moved under force of rotor rotating in the fan, and so which axial and radial speeds increased gradually. When they moved to the volute, their speeds were decreased and their moving directions were changed. Most of chaffies and straws exhausted along the upper wall of fan. Part of fan power was consumed by airflow taking chaffies and short straws and their eddy moving. Because noise was part of power consume, according to the results of numerical simulation, the test was done about the effect of muffle fixed at exit of the fan on fan noise and fan noise was decreased. The results are beneficial to decrease power consume of fan.