The reasonable flow field is the key problem in cathode design and the foundation of process stabiLity in electroChemical machining. In order to improve the efficiency of cathode designing and stabiLity of process in NC precision electroChemical machining of integer impeller, a method of applying Computational Fluid Dynamics (CFD) to aid designing flow field structure of cathode has been studied. The numerical model of the three-dimension flow field was built according to the geometrical model of interelectrode gap and cathode. Then the numerical simulation of 3-D flow field was performed by using the standard k-e turbulence model when the turbulence state in electroChemical machining had been determined. The effect of cathode's structure on the electrolyte flow field was analyzed according to the results of numerical simulation. A series of results similar to the actual experimental results are obtained. The method deduced in this paper could be used to achieve high efficiency and low cost cathode design, and consequently a lot of "trial and error" cycles will be deduced.