Abstract: The three-dimensional flow theory of turbomachinery was adopted to improve the design of 6D100-150 type water injection pump impeller,which was originally designed by using traditional one-dimensional flow theory.Comparative tests were made with the 3-D impeller and the original one installed in the same diffuser.When the pump speed was reduced to 50%,the single stage pump efficiency with the 3-D impeller was raised from 64.6% to 67.2%,the single stage pump head at the best efficiency point was raised from 33m to 35.25m.Greater improvement will be expected at full pump speed.The traditional pump design should be up-dated with advanced hydraulic calculation and there exists great potential for using the threedimensional flow theory in pump deign.