Numerical study of three-dimensional flow field was carried out for the duct system of the floor standing air-conditioner. Comparative study on three types of structure of bell mouth used in the multi-blade centrifugal fan was implemented. Calculation results show that

both the first type of bell mouths with the inward inlet whose axial height is larger than the existing type and the second type of bell mouth with new mold line inward inlet and smaller slope angle than the existing type can improve airflow utilization ratio and reduce the vortex in the back of volute exit compared to the existing type

and the air volume is increased by 6.8% and 4.2% respectively. The experiment was carried out to validate the result of simulation and the experimental results show that the air volume can increase by 4.7% and 3% respectively while the level of noise is invariant.