This paper studies the aerodynamics of the cantilever multistage centrifugal fan and analyzes the influences of changing the outlet geometric angle of the reflux device and the inlet geometric angle of the impeller blade on the inflow angle of the impeller and the performance of the fan. Based on the comparative analysis of the aerodynamic calculation results and the experimental results, the fitting curves and the calculating formula for the relation between pressure and flow and the relationship between power and flow were given. The results show that pressure curve of the centrifugal fan tends to be steeper by reducing the inlet geometric angle of the impeller blade, and the energy consumption increases by increasing the outlet geometric angle of the reflux device blade. In short, the paper proposes a method that can apply to the design and improvement of the cantilever multistage centrifugal fan.