Abstract: The G4-73 backward-inclined centrifugal fan was numerically simulated using three-dimensional elliptic governing equations and entropy theory to calculate the characteristics of flow field and entropy generation.Numerical model was validated by experimental results.The results show that entropy generation at impeller is the most in the fan,and mainly caused by turbulent dissipation,while the entropy generation caused by viscous dissipation can nearly be ignored.Impeller structural parameters were optimized,while the entropy generation and flow field were compared before and after optimization.The results show that after the impeller is optimized,entropy generation at impeller and volute reduces significantly and the flow in fan is improved.Total pressure of optimized fan increases and high efficiency area is broadened.With the increase of flow,total pressure increases more than the original fan.The total pressure and efficiency increases by 68Pa and 0.5% separately at the maximum efficiency point.The impeller optimization has important practical significance of energy-saving,solving lower pressure and CO2 emission for power plant.