Abstract: Abstract: Centrifugal pumps are widely used in general machines and the demand of the efficiency and the stable operation can be more and more high. All kinds of clearance appear easily in the centrifugal pump, such as the tip clearance and wear-ring clearance. Meantime, the gap flow of tip clearance and wear-ring clearance results in the complicated turbulent flow and clearance vortex easily which has a great effect on the hydraulic performance of a centrifugal pump and operation stability. Thus, the study of the gap clearance flow mechanism in the centrifugal pump is important. The half-height diffuser can be widely used in compressors and fans and can improve the performance of the compressors and fans. However, the application of the half-height diffuser in the centrifugal pump can be seldom and the influence law of the clearance of the half -height guide vane on the hydraulic performance of the centrifugal pump may be not clear. For the first time, the half-height diffuser is introduced into the centrifugal pump in the paper. Based on the numerical simulation and experimental methods, using SST k -ω model, research on effect of the hydraulic performance and the internal flow field of centrifugal pump with half guide vane end clearance was conducted. This paper mainly discusses the influence on the performance of a centrifugal pump with half guide vane end clearance. The results show that the appropriate half guide vane end clearance can effectively improve the centrifugal pump hydraulic performance, broaden its high efficient area. When the guide leaf height is 1.0, the maximum efficiency point is located at 37.5 m3/h, however, it can be at m3/h when the guide leaf height can be 0-0.8. The effect of the interaction between rotor and stator can be the main reason for the internal flow field of the general guide vane centrifugal pump, and the high pressure zone of the impeller outlet channel occurs when the impeller blade is near the leading edge of the guide vane. the asymmetric geometry of the volute is the main factors which impact on the internal flow field of the centrifugal pump with the end face gap. The impeller blade load in the conventional guide vane centrifugal pump is affected by the wake flow-jet is higher than that of the centrifugal pump with the half guide vane. With guide vane end gap of 0.4-0.6 of guide leaf height, the efficiency and the head of the centrifugal pump were optimal, and the maximum efficiency is 57.5%. In low flow condition, the hydraulic performance of impeller and diffuser was the key factor of influence on hydraulic performance of centrifugal pump. the total pressure loss of the impeller in the centrifugal pump with the half-height guide vane end gap is higher than that of the ordinal diffuser centrifugal pump at the 0.6 times flow conditions, 0.8 times flow conditions and 1.0 times flow conditions, however, the total pressure loss of the impeller in the centrifugal pump with the half-height guide vane end gap is lower than that of the ordinal guide vane centrifugal pump at 1.2 times flow condition and 1.4 times flow condition. The performance of the impeller when guide leaf height is 1.0 can be 7m lower than that when guide leaf height can be 0-0.8 at the 0.6 times condition. Meantime, the total pressure loss of diffuser while guide leaf height are 0-0.8 can be 6.66 m and 4.47 m high than those as 1.0 of guide leaf height at the 0.6 times and times conditions respectively. The total pressure loss of the volute in the centrifugal pump with the end clearance of the guide vane is less than that of the ordinal guide vane centrifugal pump. With the flow rate increasing, the influence of the interaction between impeller and diffuser on the centrifugal pump with the half-height guide vane decreases gradually, and the effect of the interaction between impeller and volute tongue on the centrifugal pump with the half-height guide vane increases gradually. The results provide theoretical basis and new ideas for the design and reconstruction of the guide vanes in centrifugal pumps.