This paper focuses on the efficiency improvement of a centrifugal fan used in a vacuum cleaner. In order to check the performance of the centrifugal fan system, computational fluid dynamics (CFD) analysis is used. The numerical simulation with CFD tool is carried out with RNG k−ε two-equation turbulence model based on Reynolds-averaged Navier–Stokes equations. To perform the coupling between rotating impeller and stationary area, the multiple reference frame (MRF) model is used. The numerical results of the fan are validated against with experimental results and are found to be highly reliable. The design and optimization of diffuser and impeller of a centrifugal fan are realized by using numerical investigations. For reducing the kinetic energy loss inside the fan, a guide baffle is added to optimize diffuser. The optimization results show that overall efficiency of the fan is improved by 5.27% and considering the lower efficiency of impeller caused by blockage at the blade inlet, etc., the design of impeller with long-short blades is proposed. Several cases of affecting factors under different operating conditions are simulated. Relative length (denoted as σ) and circumferential position of short blades are chosen as design variables. It is found that the efficiency of a fan with a relative length of 0.7 can be increased by 9.34%, and the best circumferential position of short blades is between two adjacent long blades.