Electrochemical machining (ECM) is one of the important technol ogies in production of aero engine blisk. The cathode modification is an import ant pa r t of the processing technology. In order to improve the modification precision o f cathode， a new method based on normal direction of constant sampling points is presented. The 1 D coordinate system along the normal direction of sampling po in ts is established. The basic cathode surface， machining error and correction val ue are calculated in the coordinate system. The position deviation of machining error and correction value is eliminated by using the new method. In order to te st the validity of the cathode modification method， experimental investigations of blisk processing are carried out by using a self designed blisk ECM system. T he machining samples are detected by the three coordinate measuring machine. A f ter one modification of cathode， the accuracy of ECM blade is increased from 0. 25 mm to 0.04 mm . Experimental results verify the feasibility and effectiveness of the new catho de modification method.