Abstract: The present work is an experimental investigation of confined water jet in jet pump.The confined jet in a converging conical inlet and in a constant-diameter pipe of the jet pump is measured by particle imagine velocimetry(PIV).The throat-to-nozzle area ratio of jet pump is 4.75.The Reynolds number based on nozzle outlet velocity and nozzle diameter D of jet pump is 3.68×10⁵.The effect of flow rates on flow field of jet pump is studied by changing the flow rates from 0.20 to 0.80.Velocity vectors,centerline velocity decays and axial velocity contours on the symmetry plate of the jet pump are obtained for four flow rates of 0.20,0.35,0.60,0.80 within a length of X/D=13.8.The results show that the confined jet in jet pump depends strongly on the flow rates when the area ratio is fixed.The smaller the flow ratio is,the quicker the centerline velocity decays are,and the shorter the jet's length of the high-velocity zone is.All results obtained in this paper provide a reliable basis for theoretical study and optimal design of jet pumps.