Abstract: In order to perfect internal flow law of double suction pump with semi-volute suction chamber and improve its anti-cavitation performance and efficiency,numerical simulation was conducted on the three dimensional steady turbulent flow in the whole flow passage of semi-volute suction chamber.The impact on hydraulic performance of double suction pump with semi-volute suction chamber by guide plate is analyzed.And result was obtained by contrasting three kinds of semi-volute suction chambers with structural differences.Using standard k-ε turbulent model and based on the Navier-stokes equation,numerical simulation and analysis were conducted by SIMPLEC method and commercial CFD software CFX.By numerical computation,the velocity and pressure distributions of the interior flow field was analyzed,which revealed the flow principle inside the semi-volute suction chamber,the hydraulic performance and the hydraulic losses of double suction pump with semi-volute suction chamber was obtained.The results show that the offset guide plate can improve the internal flow law of semi-volute suction chamber,and can reduce the imports of the vortex impeller and hydraulic loss.Finally,the application examples from practical tests favorably validated the result s of simulation,,which provide theoretical basis for improving the design.