Poor air flow patterns and vortices can affect the efficient flow of forage. To improve the working efficiency of an impeller blower, the 3-D air flows in the impeller blower of a 9R-40 rubbing and breaking machine was numerically simulated and analyzed with computation fluid dynamics (CFD) software Fluent 6.3. Then the numerical simulated results of air flow velocities in the blowing pipe were compared with their testing results to validate the reliability of the numerical simulated results. At the same time, some main geometrical parameters were simulated, which included the numbers of blade, the mounting angle of blade, the shape of housing and the arc-radius of outlet of housing etc. The optimum results were obtained according to the simulated results. The study results showed that with 4-blade, blades slanted backwards, and circular housing, impeller blowers produced more efficient air flow respectively than impeller blowers with 3-blade, blades slanted forwards and radial blades, and non-circular housing.