In order to investigate the performance change law of centrifugal refrigeration compressor under the design condition of small labyrinth seal clearance,a centrifugal refrigeration compressor was taken as the research object,and the flow in compressor impeller and labyrinth seal was simulated by CFD method.The results show that the gas pressure in the labyrinth seal decreases approximately in a ladder shape.When the inlet flow rate of impellers is the same,with the increase of seal clearance,the leakage rate and leakage loss coefficient increase greatly under the condition of small flow rate.Under the same seal clearance, as the inlet flow rate decreases, the leakage and the leakage loss coefficient increase.After considering the sealing,the total pressure ratio and isentropic efficiency of compressor are reduced,and the larger the seal clearance,the more the reduction.Especially under the condition of small flow,the total pressure ratio and isentropic efficiency decrease more obviously.The total pressure ratio is reduced by 802% at most,the isentropic efficiency is reduced by 46% at most.