In this paper,the internal flow field in a centrifugal pump working at the design flow rate operating condition has been measured using the particle image velocimetry(PIV)technique with the fluorescent particles and the index-matched fluid technology.The index-marching fluid with the same refractive index as the transparent material has been prepared and applied in the present test of pump with geometrical complex walls.The comparison between velocity distributions of PIV results both with and without fluorescent particles,as well as with and without index-marching fluid are conducted to find the differences.The DES(Detached Eddy Simulation)has been employed to calculate the three-dimensional unsteady turbulent flow in the pump to examine and to certify the PIV measurement results.The DES results of instantaneous flow velocity fields agree with PIV test results with fluorescent particles and index-marching fluid.It is necessary to perform the PIV measurement of pumps with fluorescent seeds and index-marching fluid in order to get exact results.The experimental results show the distributions of velocity,steamlines,and the principal Reynolds normal stress(PRNS)and the principal Reynolds shear stress(PRSS). In this paper, the internal flow field in a centrifugal pump working at the design flow rate operating condition has been measured using the particle image velocimetry (PIV) technique with the fluorescent particles and the index-matched fluid technology. The index-marching fluid with the same refractive index as the transparent material has been prepared and applied in the present test of pump with geometrical complex walls. The comparison between velocity distributions of PIV results both with and without fluorescent particles, as well as with and without index-marching fluid are conducted to find the differences. The DES (Detached Eddy Simulation) has been employed to calculate the three-dimensional unsteady turbulent flow in the pump to examine and to certify the PIV measurement results. The DES results of instantaneous flow velocity fields agree with PIV test results with fluorescent particles and index-marching fluid. It is necessary to perform the PIV measurement of pumps with fluorescent s eeds and index-marching fluid in order to get exact results. The experimental results show the distributions of velocity, steamlines, and the principal Reynolds normal stress (PRNS) and the principal Reynolds shear stress (PRSS).